Terminal device, base station device, and uplink response signal transmission method

ABSTRACT

When downlink data allocation is indicated in an ePDCCH, this terminal device can determine PUCCH resources to be used in notification of response signals indicating results of error detection of downlink data without imposing scheduling restrictions on future DL subframes. In this device, an extraction unit receives downlink data on multiple unit bands. A CRC unit detects errors in the downlink data. A response signal generation unit generates a response signal by using the results of error detection of the downlink data obtained by the CRC unit. The control unit arranges the response signal in the PUCCH resources corresponding to the current DL subframe.

BACKGROUND Technical Field

The present invention relates to a terminal apparatus, a base stationapparatus and a transmission method.

Description of the Related Art

3GPP LTE employs Orthogonal Frequency Division Multiple Access (OFDMA)as a downlink communication scheme. In radio communication systems towhich 3GPP LTE is applied, base stations transmit synchronizationsignals (i.e., Synchronization Channel: SCH) and broadcast signals(i.e., Broadcast Channel: BCH) using predetermined communicationresources. Meanwhile, each terminal finds an SCH first and therebyensures synchronization with the base station. Subsequently, theterminal reads BCH information to acquire base station-specificparameters (e.g., frequency bandwidth) (see Non-Patent Literature(hereinafter, abbreviated as NPL) 1, 2 and 3).

In addition, upon completion of the acquisition of the basestation-specific parameters, each terminal sends a connection request tothe base station to thereby establish a communication link with the basestation. The base station transmits control information via PhysicalDownlink Control CHannel (PDCCH) as appropriate to the terminal withwhich a communication link has been established via a downlink controlchannel or the like.

The terminal performs “blind-determination” on each of a plurality ofpieces of control information included in the received PDCCH signal(i.e., Downlink (DL) Assignment Control Information: also referred to asDownlink Control Information (DCI)). More specifically, each piece ofthe control information includes a Cyclic Redundancy Check (CRC) partand the base station masks this CRC part using the terminal ID of thetransmission target terminal. Accordingly, until the terminal demasksthe CRC part of the received piece of control information with its ownterminal ID, the terminal cannot determine whether or not the piece ofcontrol information is intended for the terminal. In thisblind-determination, if the result of demasking the CRC part indicatesthat the CRC operation is OK, the piece of control information isdetermined as being intended for the terminal.

Moreover, in 3GPP LTE, Automatic Repeat Request (ARQ) is applied todownlink data to terminals from a base station. More specifically, eachterminal feeds back a response signal indicating the result of errordetection on the downlink data to the base station. Each terminalperforms a CRC on the downlink data and feeds back Acknowledgment (ACK)when CRC=OK (no error) or Negative Acknowledgment (NACK) when CRC=Not OK(error) to the base station as a response signal. An uplink controlchannel such as Physical Uplink Control Channel (PUCCH) is used to feedback the response signals (i.e., ACK/NACK signals (hereinafter, may bereferred to as “A/N,” simply)).

The control information to be transmitted from a base station hereinincludes resource assignment information including information onresources assigned to the terminal by the base station. As describedabove, PDCCH is used to transmit this control information. This PDCCHincludes one or more L1/L2 control channels (L1/L2 CCH). Each L1/L2 CCHconsists of one or more Control Channel Elements (CCE). Morespecifically, a CCE is the basic unit used to map the controlinformation to PDCCH. Moreover, when a single L1/L2 CCH consists of aplurality of CCEs (2, 4 or 8), a plurality of contiguous CCEs startingfrom a CCE having an even index are assigned to the L1/L2 CCH. The basestation assigns the L1/L2 CCH to the resource assignment target terminalin accordance with the number of CCEs required for indicating thecontrol information to the resource assignment target terminal. The basestation maps the control information to physical resources correspondingto the CCEs of the L1/L2 CCH and transmits the mapped controlinformation.

In addition, CCEs are associated with component resources of PUCCH(hereinafter, may be referred to as “PUCCH resource”) in a one-to-onecorrespondence. Accordingly, a terminal that has received an L1/L2 CCHidentifies the component resources of PUCCH that correspond to the CCEsforming the L1/L2 CCH and transmits a response signal to the basestation using the identified resources. However, when the L1/L2 CCHoccupies a plurality of contiguous CCEs, the terminal transmits theresponse signal to the base station using a PUCCH component resourcecorresponding to a CCE having a smallest index among the plurality ofPUCCH component resources respectively corresponding to the plurality ofCCEs (i.e., PUCCH component resource associated with a CCE having aneven numbered CCE index). In this manner, the downlink communicationresources are efficiently used.

As illustrated in FIG. 1, a plurality of response signals transmittedfrom a plurality of terminals are spread using a Zero Auto-correlation(ZAC) sequence having the characteristic of zero autocorrelation in atime-domain, a Walsh sequence and a discrete Fourier transform (DFT)sequence, and are code-multiplexed in a PUCCH. In FIG. 1, (W₀, W₁, W₂,W₃) represent a length-4 Walsh sequence and (F₀, F₁, F₂) represent alength-3 DFT sequence. As illustrated in FIG. 1, ACK or NACK responsesignals are primary-spread over frequency components corresponding to 1SC-FDMA symbol by a ZAC sequence (length-12) in frequency-domain. Morespecifically, the length-12 ZAC sequence is multiplied by a responsesignal component represented by a complex number.

Subsequently, the ZAC sequence serving as the response signals andreference signals after the primary-spread is secondary-spread inassociation with each of a Walsh sequence (length-4: W₀-W₃ (may bereferred to as Walsh Code Sequence)) and a DFT sequence (length-3:F₀-F₂). More specifically, each component of the signals of length-12(i.e., response signals after primary-spread or ZAC sequence serving asreference signals (i.e., Reference Signal Sequence) is multiplied byeach component of an orthogonal code sequence (i.e., orthogonalsequence: Walsh sequence or DFT sequence). Moreover, thesecondary-spread signals are transformed into signals of length-12 inthe time-domain by inverse fast Fourier transform (IFFT). A CP is addedto each signal obtained by IFFT processing, and the signals of one slotconsisting of seven SC-FDMA symbols are thus formed.

The response signals from different terminals are spread using ZACsequences each corresponding to a different cyclic shift value (i.e.,index) or orthogonal code sequences each corresponding to a differentsequence number (i.e., orthogonal cover index (OC index)). An orthogonalcode sequence is a combination of a Walsh sequence and a DFT sequence.In addition, an orthogonal code sequence is referred to as a block-wisespreading code in some cases. Thus, base stations can demultiplex thecode-multiplexed plurality of response signals using the related artdespreading and correlation processing (see NPL 4).

However, it is not necessarily true that each terminal succeeds inreceiving a downlink assignment control signal, because the terminalperforms blind-determination in each subframe to find a downlinkassignment control signal intended for the terminal. When the terminalfails to receive the downlink assignment control signal intended for theterminal on a certain downlink component carrier, the terminal would noteven know whether or not there is downlink data intended for theterminal on the downlink component carrier. Accordingly, when a terminalfails to receive the downlink assignment control signal intended for theterminal on a certain downlink component carrier, the terminal generatesno response signals for the downlink data on the downlink componentcarrier. This error case is defined as discontinuous transmission ofACK/NACK signals (DTX of response signals) in the sense that theterminal transmits no response signals.

In 3GPP LTE systems (may be referred to as “LTE system,” hereinafter),base stations assign resources to uplink data and downlink data,independently. For this reason, in the 3GPP LTE system, terminals (i.e.,terminals compliant with LTE system (hereinafter, referred to as “LTEterminal”)) encounter a situation where the terminals need to transmituplink data and response signals for downlink data simultaneously in theuplink. In this situation, the response signals and uplink data from theterminals are transmitted using time-division multiplexing (TDM). Asdescribed above, the single carrier properties of transmission waveformsof the terminals are maintained by the simultaneous transmission ofresponse signals and uplink data using TDM.

In addition, as illustrated in FIG. 2, the response signals (i.e.,“A/N”) transmitted from each terminal partially occupy the resourcesassigned to uplink data (i.e., Physical Uplink Shared CHannel (PUSCH)resources) (i.e., response signals occupy some SC-FDMA symbols adjacentto SC-FDMA symbols to which reference signals (RS) are mapped) and arethereby transmitted to a base station in time-division multiplexing(TDM). However, “subcarriers” in the vertical axis in FIG. 2 are alsotermed as “virtual subcarriers” or “time contiguous signals,” and “timecontiguous signals” that are collectively inputted to a discrete Fouriertransform (DFT) circuit in a SC-FDMA transmitter are represented as“subcarriers” for convenience. More specifically, optional data of theuplink data is punctured due to the response signals in the PUSCHresources. Accordingly, the quality of uplink data (e.g., coding gain)is significantly reduced due to the punctured bits of the coded uplinkdata. For this reason, base stations instruct the terminals to use avery low coding rate and/or to use very large transmission power so asto compensate for the reduced quality of the uplink data due to thepuncturing.

Meanwhile, the standardization of 3GPP LTE-Advanced for realizing fastercommunication than 3GPP LTE is in progress. 3GPP LTE-Advanced systems(may be referred to as “LTE-A system,” hereinafter) follow LTE systems.3GPP LTE-Advanced will introduce base stations and terminals capable ofcommunicating with each other using a wideband frequency of 40 MHz orgreater to realize a downlink transmission rate of up to 1 Gbps orabove.

In the LTE-A system, in order to simultaneously achieve backwardcompatibility with the LTE system and ultra-high-speed communicationseveral times faster than transmission rates in the LTE system, theLTE-A system band is divided into “component carriers” of 20 MHz orbelow, which is the bandwidth supported by the LTE system. In otherwords, the “component carrier” is defined herein as a band having amaximum width of 20 MHz and as the basic unit of communication band. Inthe Frequency Division Duplex (FDD) system, moreover, “componentcarrier” in downlink (hereinafter, referred to as “downlink componentcarrier”) is defined as a band obtained by dividing a band according todownlink frequency bandwidth information in a BCH broadcasted from abase station or as a band defined by a distribution width when adownlink control channel (PDCCH) is distributed in the frequency domain.In addition, “component carrier” in uplink (hereinafter, referred to as“uplink component carrier”) may be defined as a band obtained bydividing a band according to uplink frequency band information in a BCHbroadcasted from a base station or as the basic unit of a communicationband of 20 MHz or below including a Physical Uplink Shared CHannel(PUSCH) in the vicinity of the center of the bandwidth and PUCCH s forLTE on both ends of the band. In addition, the term “component carrier”may be also referred to as “cell” in English in 3GPP LTE-Advanced.Furthermore, “component carrier” may also be abbreviated as CC(s).

In the Time Division Duplex (TDD) system, a downlink component carrierand an uplink component carrier have the same frequency band, anddownlink communication and uplink communication are realized byswitching between the downlink and uplink on a time division basis. Forthis reason, in the case of the TDD system, the downlink componentcarrier can also be expressed as “downlink communication timing in acomponent carrier.” The uplink component carrier can also be expressedas “uplink communication timing in a component carrier.” The downlinkcomponent carrier and the uplink component carrier are switched based ona UL-DL configuration as shown in FIG. 3. In the UL-DL configurationshown in FIG. 3, timings are configured in subframe units (that is, 1msec units) for downlink communication (DL) and uplink communication(UL) per frame (10 msec). The UL-DL configuration can construct acommunication system capable of flexibly meeting a downlinkcommunication throughput requirement and an uplink communicationthroughput requirement by changing a subframe ratio between downlinkcommunication and uplink communication. For example, FIG. 3 illustratesUL-DL configurations (Config 0 to 6) having different subframe ratiosbetween downlink communication and uplink communication. In addition, inFIG. 3, a downlink communication subframe is represented by “D,” anuplink communication subframe is represented by “U” and a specialsubframe is represented by “S.” Here, the special subframe is a subframeat the time of switchover from a downlink communication subframe to anuplink communication subframe. In the special subframe, downlink datacommunication may be performed as in the case of the downlinkcommunication subframe. In each UL-DL configuration shown in FIG. 3,subframes (20 subframes) corresponding to 2 frames are expressed in twostages: subframes (“D” and “S” in the upper row) used for downlinkcommunication and subframes (“U” in the lower row) used for uplinkcommunication.

Furthermore, as shown in FIG. 3, an error detection result correspondingto downlink data (ACK/NACK) is indicated in the fourth uplinkcommunication subframe or an uplink communication subframe after thefourth subframe from the subframe to which the downlink data isassigned. In the TDD system, it is necessary to transmit responsesignals indicating error detection results corresponding to downlinkdata which has been indicated in a plurality of downlink communicationsubframes collectively in one uplink communication subframe. The numberof downlink communication subframes at this time (which may also becalled “bundling window”) is represented by M and an index of a downlinkcommunication subframe corresponding to one uplink communicationsubframe is represented by m. For example, in UL-DL Configuration #2,error detection results on downlink data in four downlink communicationsubframes SF #4, 5, 6 and 8 of a first frame are indicated in uplinkcommunication subframe SF #3 of a second frame. In this case, M=4, andSF #4, 5, 6 and 8 of the first frame correspond to m=0, 1, 2 and 3respectively.

In TDD in an LTE-A system, a terminal receives downlink assignmentcontrol information via PDCCH and transmits a response signal over anuplink upon receiving downlink data. The following two methods areadopted as the method of transmitting the response signals.

Method 1 is a method (implicit signaling) whereby a terminal transmits aresponse signal using a PUCCH resource associated, in a one-to-onecorrespondence, with leading CCE index n_(CCE) of CCE (Control ChannelElement) occupied by PDCCH and index m of a downlink communicationsubframe corresponding to one uplink communication subframe (see PTL 1).Note that m is indexed in time sequence.

More specifically, the terminal first calculates parameter c={0, 1, 2,3} that satisfies equation 1 in a magnitude relationship between leadingCCE index n_(CCE) occupied by PDCCH intended for the terminal (DLassignment) and N_(c) for each DL subframe m. Note that Nc in equation 1is calculated according to equation 2. N^(DL) _(RB) in equation 2 is thenumber of downlink resource blocks and N^(RB) _(SC) is the number ofsubcarriers per resource block. The terminal then determines PUCCHresources n⁽¹⁾ _(PUCCH) based on DL subframe m and calculated caccording to equation 3 (see NPL 3). Note that N⁽¹⁾ _(PUCCH) in equation3 is an offset value for all PUCCH resources and is a value set in theterminal in advance.[1]N _(c) ≤n _(CCE) <N _(c+1)  (Equation 1)[2]N _(c)=max{0,└[N _(RB) ^(DL)·(N _(sc) ^(RB) ·c−4)]/36┘}  (Equation 2)[3]n _(PUCCH,j) ⁽¹⁾=(M−m−1)·N _(c) +m·N _(c+1) +n _(CCE,m) +N _(PUCCH)⁽¹⁾  (Equation 3)

As shown in FIG. 4, in TDD, PUCCH resource region 10 corresponding toPDCCH is divided for each c and each partial region corresponding to cis divided for each m. PUCCH resources for each c and each m arearranged from a frequency end direction toward the center direction of acomponent carrier in ascending order of m and in ascending order of c.

In the example of FIG. 4, when transmitting a response signal indicatingan error detection result corresponding to downlink data indicated in asubframe with m=2, the terminal first calculates c from a magnituderelationship between leading CCE index n_(CCE) occupied by PDCCH (DLassignment) intended for the terminal and N_(c) in virtual PUCCHresource region 50 that collects PUCCH resources corresponding to thesubframe with m=2 (equation 1).

Next, the terminal arranges the response signal in PUCCH resource n⁽¹⁾_(PUCCH) (reference numeral 11 in FIG. 4) in actual PUCCH resourceregion 10 for the acquired c (c=0 in FIG. 4) (equation 3).

The range of c used here extends as the CCE index increases. A maximumvalue of the CCE index increases as the scale of the PDCCH regionincreases. Therefore, the greater the range of c used, the greater thePDCCH region becomes. The scale of the PDCCH region is defined by CFI(Control Format Indicator). For example, the PDCCH region is composed ofthree OFDM symbols when CFI=3, and it is therefore largest, whereas whenCFI=1, the PDCCH region is composed of one OFDM symbol, and it istherefore smallest. Furthermore, CFI is dynamically indicated to theterminal for every subframe. Therefore, the PUCCH resource region isused more frequently when c is smaller. For this reason, the occupancyof control information in the PUCCH resource region increases as cdecreases and decreases as c increases.

In the LTE-A system, a control signal may be transmitted using aplurality of PUCCH resources by applying transmission diversity orapplying channel selection during carrier aggregation. In this case, asshown in equation 4 and FIG. 5, method 1 uses a predetermined PUCCHresource (reference numeral 11 in FIG. 5) and a PUCCH resource(reference numeral 12 in FIG. 5) adjacent to the PUCCH resource (whichbecomes n_(CCE)+1 with respect to n_(CCE)) in the actual PUCCH resourceregion. In other words, in the LTE-A system, an offset of +1 is added tothe CCE index in the actual PUCCH resource region.[4]n _(PUCCH,j+1) ⁽¹⁾=(M−m−1)·N _(c) +m·N _(c+1) +n _(CCE,m)+1+N _(PUCCH)⁽¹⁾  (Equation 4)

Method 2 is a method (explicit signaling) whereby a base stationindicates PUCCH resources to a terminal in advance and the terminaltransmits a response signal using the PUCCH resources indicated inadvance from the base station.

According to method 2, the base station can dynamically indicate to theterminal, information (ARI (Ack/Nack Resource Indicator)) indicating onePUCCH resource from among a plurality of PUCCH resources through DLassignment in advance. This makes it possible to dynamically switchbetween quasi-static PUCCH resources with a small number of bits. Forexample, when ARI has 2 bits, the base station can select one of fourPUCCH resources.

In the LTE-A system, various devices are introduced as radiocommunication terminals such as M2M (Machine to Machine) communication,and the number of multiplexed terminals tends to increase by MIMOtransmission techniques, and therefore the number of control signalstransmitted from a base station to a terminal is considered to increase.For this reason, there may not be enough PDCCH regions which are regionsin which PDCCHs used for control signals are mapped. When the basestation cannot transmit control signals due to this shortage ofresources, the base station can no longer assign data to the terminal.For this reason, the terminal can no longer use a PUSCH region to beused for data even if the PUSCH region is free and the system throughputmay deteriorate.

As a method of solving this shortage of resources, studies are beingcarried out on the possibility of mapping control signals intended forterminals under a base station to a PDSCH region as well. This region inwhich control signals intended for terminals under the base station aremapped, that is, a region available to both control signals and data iscalled “enhanced PDCCH (ePDCCH) region.” Thus, the base station cantransmit more control signals to terminals by providing ePDCCHs, and canthereby realize various kinds of control. For example, the base stationcan perform transmission power control on control signals transmitted toa terminal located near a cell edge or control of interference oftransmitted control signals with another cell or control of interferenceof another cell with the cell formed by the base station.

In LTE, DL assignment instructing downlink data assignment (PDSCH) andUL grant instructing uplink data assignment are transmitted using PDCCH.

In LTE-Advanced, DL assignment and UL grant are transmitted also usingePDCCH in the same way as PDCCH. Studies are being carried out on thepossibility that resources to which DL assignment is mapped andresources to which UL grant is mapped will be divided on the frequencyaxis in an ePDCCH region.

Methods 1 and 2 described above are defined as the method of determiningPUCCH resources in a PUCCH resource region when DL assignment isindicated in a PDCCH region (hereinafter referred to as “PDCCH-PUCCHresource region”). Furthermore, in method 2, it is defined that a presetPUCCH resource is selected by dynamic ARI.

Here, when a PUCCH resource region in the case where DL assignment isindicated in an ePDCCH region (hereinafter referred to as “ePDCCH-PUCCHresource region”) is secured aside from a PDCCH-PUCCH resource region,the total amount of the PUCCH resource region increases. Especially whencarrier aggregation is applied, PUCCH is transmitted using only one cellto avoid PAPR (Peak-to-Average Power Ratio) of the terminal fromincreasing. The cell is always PCell. PCell is generally a macro cellhaving a large coverage, and high mobility is secured by a macro celltransmitting PUCCH. The capacity of PUCCH resources may be tight in thefuture due to not only introduction of ePDCCH but also introduction ofcarrier aggregation or introduction of M2M whereby many terminalsperform data communication. Thus, in the LTE-A system, studies are beingcarried out on operation of causing ePDCCH-PUCCH resource regions tooverlap with PDCCH-PUCCH resource regions.

As a method of determining ePDCCH-PUCCH resources, a method ofinstructing a preset offset value for an eCCE index using ARI or amethod of defining a fixed value (equation 5) (see NPL 5) may be used.According to these methods, the base station first determines whether ornot ePDCCH-PUCCH resources with offset value 0, that is, throughimplicit signaling, collide with PDCCH-PUCCH resources. When nocollision occurs, the base station indicates ARI=0 to the terminal so asto use the ePDCCH-PUCCH resources. On the other hand, when collisionoccurs, the base station sequentially determines collision or nocollision using ePDCCH-PUCCH resources with other offset values addedthereto and indicates ARI or a fixed value corresponding to anon-colliding ePDCCH-PUCCH resource to the terminal.[5]n _(PUCCH) ^(E) =n _(E−CCE) +N _(PUCCH) ⁽¹⁾+ARI  (Equation 5)

In ePDCCH, values such as 4, 8, 16, 32 are taken as scale N_(eCCE) ofone ePDCCH search space. However, values such as 2, 4, 8, 16 are takenas N_(eCCE) in the case of a special subframe where the number of OFDMsymbols to be used for the downlink is small (that is, the case where aconfiguration with a small number of OFDM symbols to be used for thedownlink is set as a special subframe configuration in which the numberof OFDM symbols to be used for downlink communication in a specialsubframe, a gap (downlink/uplink switching period) and a ratio of thenumber of OFDM symbols to be used for uplink communication are set).Furthermore, the base station can set ePDCCH search space sets which aredifferent between terminals, and these ePDCCH search space sets may havedifferent sizes. The base station can further set a plurality of ePDCCHsearch space sets in one terminal, and these ePDCCH search space setsmay have different scales. The base station can further set N⁽¹⁾_(PUCCH) as start positions of different PUCCH resources for therespective ePDCCH search space sets.

CITATION LIST Patent Literature

PTL 1

Japanese Unexamined Patent Application Publication (Translation of PCTApplication) No. 2011-507704

Non-Patent Literature

NPL 1

3GPP TS 36.211 V10.1.0, “Physical Channels and Modulation (Release 10),”March 2011

NPL 2

3GPP TS 36.212 V10.1.0, “Multiplexing and channel coding (Release 10),”March 2011

NPL 3

3GPP TS 36.213 V10.1.0, “Physical layer procedures (Release 10),” March2011

NPL 4

Seigo Nakao, Tomofumi Takata, Daichi Imamura, and Katsuhiko Hiramatsu,“Performance enhancement of E-UTRA uplink control channel in fast fadingenvironments,” Proceeding of IEEE VTC 2009 spring, April 2009

NPL 5

Samsung, 3GPP RANI meeting #68bis, R1-121647, “HARQ-ACK PUCCH Resourcesin Response to E-PDCCH Detections,” March 2012

BRIEF SUMMARY Technical Problem

As shown in FIG. 6, ePDCCH-PUCCH resource region 20 may be divided foreach c′ and each m as in the case of PDCCH-PUCCH resource region 10shown in FIGS. 4 and 5. At this time, PUCCH resources are arranged inascending order of m and in ascending order of c′ from the frequency enddirection to center direction of a component carrier. When ARI has 2bits, one of four different offset values δ₀(=0), δ₁, δ₂ and δ₃ isindicated to the terminal. At least two offset values are greater than“+1.” For this reason, when m for a DL subframe at certain timing isassumed to be m_(current), the possibility that a PUCCH resource as theoffset destination may become m>m_(current) is higher than “+1” which isthe offset value applicable in the PDCCH-PUCCH resource region.

For example, in FIG. 6, when m=1, suppose ePDCCH-PUCCH resource 21 withoffset value δ₀=0 in terminal A to which ePDCCH is indicated with eCCEindex n_(eCCE) collides with a PDCCH-PUCCH resource in another terminalB to which PDCCH is indicated with CCE index n_(CCE). In this case, thebase station determines collision or no collision regarding PUCCHresources 22, 23 and 24, which correspond to PUCCH resource 21, withoffset values δ₁, δ₂ and δ₃ added thereto respectively to avoidcollision. The base station then indicates to terminal A, one of ARI=1,2 and 3 corresponding to a resource among PUCCH resources 22, 23 and 24in which no collision has occurred. However, in the example of FIG. 6,PUCCH resource 23, which is the destination of a shift corresponding toδ₂, becomes a PUCCH resource corresponding to m=2 and PUCCH resource 24,which is the destination of a shift corresponding to δ₃, becomes a PUCCHresource corresponding to m=3. This means that at a point in time of DLsubframe m=1, control information mapped to an ePDCCH-PUCCH resourcewill occupy PUCCH resources when m=2 and m=3 which are future DLsubframes. Since PUCCH resources are associated with PDCCH and ePDCCHrespectively in a one-to-one correspondence, this means that the basestation cannot perform scheduling on the PDCCH and ePDCCH when m=2 andm=3 which are future DL subframes.

Thus, the prior art imposes constraints on scheduling for future DLsubframes when downlink data assignment is instructed by ePDCCH. Theconstraints increase as the value of m increases. Therefore, it is morelikely that the base station cannot assign control information to anoptimum terminal regarding large m. The base station may need schedulingtaking into account an interval between subframes, which may cause abase station scheduler to be more complicated.

An object of the present invention is to provide a method of determininga PUCCH resource to be used to indicate a response signal indicating anerror detection result of downlink data without imposing constraints onscheduling for future DL subframes when downlink data assignment isindicated by ePDCCH.

Solution to Problem

As described above, a terminal apparatus according to an aspect of thepresent invention is a terminal apparatus including: a control sectionthat arranges a response signal on a predetermined PUCCH resource in anuplink control channel (PUCCH) resource region corresponding to anenhanced downlink control channel (ePDCCH); and a transmitting sectionthat transmits the response signal arranged on the PUCCH resource, inwhich the PUCCH resource region is divided into a plurality of partialregions, and each of the partial regions is divided into a number ofdownlink communication subframes, PUCCH resources for each index c′ ofthe partial region and each index m indicating a time-sequential orderof the downlink communication subframe are arranged in the PUCCHresource region in ascending order of indices m and in ascending orderof indices c′, and the control section arranges a response signalcorresponding to an m-th downlink communication subframe in a PUCCHresource selected from among the PUCCH resources corresponding to theindices m and below.

A transmission method according to an aspect of the present invention isa transmission method including: making a control to arrange a responsesignal on a predetermined PUCCH resource in an uplink control channel(PUCCH) resource region corresponding to an enhanced downlink controlchannel (ePDCCH); and transmitting the response signal arranged on thePUCCH resource, in which: the PUCCH resource region is divided into aplurality of partial regions, and each of the partial regions is dividedinto a number of downlink communication subframes, PUCCH resources foreach index c′ of the partial region and each index m indicating atime-sequential order of the downlink communication subframe arearranged in the PUCCH resource region in ascending order of m and inascending order of c′, and in the making a control, a response signalcorresponding to an m-th downlink communication subframe is arranged ina PUCCH resource selected from among the PUCCH resources correspondingto the indices m and below.

Advantageous Effects of Invention

According to the present invention, when downlink data assignment isindicated by ePDCCH, it is possible to determine a PUCCH resource to beused to indicate a response signal indicating an error detection resultof downlink data without imposing constraints on scheduling for futureDL subframes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating a method of spreading response signalsand reference signals;

FIG. 2 is a diagram illustrating an operation related to a case whereTDM is applied to response signals and uplink data on PUSCH resources;

FIG. 3 is a diagram provided for describing a UL-DL configuration inTDD;

FIG. 4 is a diagram provided for describing a PDCCH-PUCCH resourceregion;

FIG. 5 is a diagram provided for describing an offset value in thePDCCH-PUCCH resource region;

FIG. 6 is a diagram provided for describing problems in the method ofdetermining ePDCCH-PUCCH resources;

FIG. 7 is a block diagram illustrating a main configuration of a basestation according to Embodiment 1 of the present invention;

FIG. 8 is a block diagram illustrating a main configuration of aterminal according to Embodiment 1 of the present invention;

FIG. 9 is a block diagram illustrating a configuration of the basestation according to Embodiment 1 of the present invention;

FIG. 10 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1 of the present invention;

FIG. 11 is a diagram provided for describing a method of determiningePDCCH-PUCCH resources according to Embodiment 1 of the presentinvention;

FIG. 12 is a diagram provided for describing a method of determiningePDCCH-PUCCH resources according to Embodiment 2 of the presentinvention;

FIG. 13 is a first diagram provided for describing variation 1 accordingto Embodiment 2 of the present invention;

FIG. 14 is a second diagram provided for describing variation 1according to Embodiment 2 of the present invention;

FIG. 15 is a diagram provided for describing variation 2 according toEmbodiment 2 of the present invention;

FIG. 16 is a diagram provided for describing variation 3 according toEmbodiment 2 of the present invention;

FIG. 17 is a first diagram provided for describing variation 4 accordingto Embodiment 2 of the present invention;

FIG. 18 is a second diagram provided for describing variation 4according to Embodiment 2 of the present invention;

FIG. 19 is a diagram provided for describing variation 6 according toEmbodiment 2 of the present invention;

FIG. 20 is a method of determining ePDCCH-PUCCH resources according toEmbodiment 3 of the present invention;

FIG. 21 is a method of determining ePDCCH-PUCCH resources according toEmbodiment 4 of the present invention;

FIG. 22 is a diagram provided for describing problems and a solutionthereof when an ePDCCH terminal and a UL CoMP terminal exist;

FIG. 23 is a first diagram provided for describing variation 7 accordingto Embodiment 2 of the present invention;

FIG. 24 is a second diagram provided for describing variation 7according to Embodiment 2 of the present invention;

FIG. 25 is a third diagram provided for describing variation 7 accordingto Embodiment 2 of the present invention;

FIG. 26 is a first diagram provided for describing a method of dividinga PUCCH resource region of variation 7 according to Embodiment 2 of thepresent invention;

FIG. 27 is a second diagram provided for describing a method of dividinga PUCCH resource region of variation 7 according to Embodiment 2 of thepresent invention;

FIG. 28 is a third diagram provided for describing a method of dividinga PUCCH resource region of variation 7 according to Embodiment 2 of thepresent invention;

FIG. 29 is a first diagram provided for describing a size of dividing aPUCCH resource region of variation 7 according to Embodiment 2 of thepresent invention;

FIG. 30 is a second diagram provided for describing a size of dividing aPUCCH resource region of variation 7 according to Embodiment 2 of thepresent invention; and

FIG. 31 is a third diagram provided for describing a size of dividing aPUCCH resource region of variation 7 according to Embodiment 2 of thepresent invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Throughout theembodiments, the same elements as those already described are assignedthe same reference numerals and any detailed description of the elementsis omitted.

Embodiment 1

FIG. 7 is a block diagram illustrating a main configuration of basestation 100 according to the present embodiment. FIG. 8 is a blockdiagram illustrating a main configuration of terminal 200 according toEmbodiment 1 of the present invention. Terminal 200 communicates withbase station 100 using a plurality of component carriers including afirst component carrier and a second component carrier. A subframeconfiguration pattern making up one frame, which is a configurationpattern (DL-UL Configuration) including a downlink communicationsubframe (DL subframe) used for downlink communication and an uplinkcommunication subframe (UL subframe) used for uplink communication isset in each component carrier set in terminal 200.

In base station 100, control section 101 determines collision or nocollision between ePDCCH-PUCCH resources and PDCCH-PUCCH resources.Control information generating section 102 indicates ARI correspondingto non-colliding ePDCCH-PUCCH resources to terminal 200.

In terminal 200, extraction section 204 receives downlink data using aplurality of component carriers. Decoding section 210 decodes downlinkdata. CRC section 211 detects an error of decoded downlink data.Response signal generating section 212 generates response signals usingan error detection result of the downlink data obtained in CRC section211. Control section 208 arranges response signals in predeterminedPUCCH resources and transmits the response signals to base station 100.

[Configuration of Base Station]

FIG. 9 is a configuration diagram of base station 100 according toEmbodiment 1 of the present invention. In FIG. 9, base station 100includes control section 101, control information generating section102, coding section 103, modulation section 104, coding section 105,data transmission controlling section 106, modulation section 107,mapping section 108, inverse fast Fourier transform (IFFT) section 109,CP adding section 110, radio transmitting section 111, radio receivingsection 112, CP removing section 113, PUCCH extracting section 114,despreading section 115, sequence controlling section 116, correlationprocessing section 117, A/N determining section 118, bundled A/Ndespreading section 119, inverse discrete Fourier transform (IDFT)section 120, bundled A/N determining section 121 and retransmissioncontrol signal generating section 122.

Control section 101 assigns a downlink resource for transmitting controlinformation (i.e., downlink control information assignment resource) anda downlink resource for transmitting downlink data (i.e., downlink dataassignment resource) for a resource assignment target terminal(hereinafter, referred to as “destination terminal” or simply“terminal”) 200. This resource assignment is performed in a downlinkcomponent carrier included in a component carrier group configured forresource assignment target terminal 200. In addition, the downlinkcontrol information assignment resource is selected from among theresources corresponding to downlink control channel (i.e., PDCCH orePDCCH) in each downlink component carrier. Moreover, the downlink dataassignment resource is selected from among the resources correspondingto downlink data channel (i.e., PDSCH) in each downlink componentcarrier. In addition, when there are a plurality of resource assignmenttarget terminals 200, control section 101 assigns different resources toterminals 200, respectively.

The downlink control information assignment resources are equivalent toL1/L2 CCH described above. More specifically, the downlink controlinformation assignment resources are each formed of one or a pluralityof CCEs or eCCEs.

Control section 101 determines whether or not ePDCCH-PUCCH resourcescollide with PDCCH-PUCCH resources, and controls control informationgenerating section 102 so as to generate ARI based on the determinationresult.

Control section 101 determines the coding rate used for transmittingcontrol information to resource assignment target terminal 200. The datasize of the control information varies depending on the coding rate.Thus, control section 101 assigns a downlink control informationassignment resource having the number of CCEs or eCCEs that allows thecontrol information having this data size to be mapped to the resource.

Control section 101 outputs information on the downlink data assignmentresource to control information generating section 102. Moreover,control section 101 outputs information on the coding rate to codingsection 103. In addition, control section 101 determines and outputs thecoding rate of transmission data (i.e., downlink data) to coding section105. Moreover, control section 101 outputs information on the downlinkdata assignment resource and downlink control information assignmentresource to mapping section 108. However, control section 101 controlsthe assignment in such a way that the downlink data and downlink controlinformation for the downlink data are mapped to the same downlinkcomponent carrier.

Control information generating section 102 generates and outputs controlinformation including the information on the downlink data assignmentresource and ARI to coding section 103. This control information isgenerated for each downlink component carrier. In addition, when thereare a plurality of resource assignment target terminals 200, the controlinformation includes the terminal ID of each destination terminal 200 inorder to distinguish resource assignment target terminals 200 from oneanother. For example, the control information includes CRC bits maskedby the terminal ID of destination terminal 200. This control informationmay be referred to as “control information carrying downlink assignment”or “downlink control information (DCI).”

Coding section 103 encodes the control information using the coding ratereceived from control section 101 and outputs the coded controlinformation to modulation section 104.

Modulation section 104 modulates the coded control information andoutputs the resultant modulation signals to mapping section 108.

Coding section 105 inserts the coding rate information from controlsection 101 into transmission data (downlink data) for each destinationterminal 200 and encodes and outputs the transmission data after theinsertion to data transmission controlling section 106. However, when aplurality of downlink component carriers are assigned to destinationterminal 200, coding section 105 encodes transmission data to betransmitted by each downlink component carrier.

Data transmission controlling section 106 outputs the coded transmissiondata to modulation section 107 and also keeps the coded transmissiondata at the initial transmission. The coded transmission data is keptfor each destination terminal 200. Transmission data to one destinationterminal 200 is kept for each downlink component carrier fortransmission. This makes it possible to perform not only retransmissioncontrol of the entire data transmitted to destination terminal 200 butalso retransmission control for each downlink component carrier.

Furthermore, upon reception of a NACK or DTX for downlink datatransmitted on a predetermined downlink component carrier fromretransmission control signal generating section 122, data transmissioncontrolling section 106 outputs the data kept in the manner describedabove and corresponding to this downlink component carrier to modulationsection 107. Upon reception of an ACK for the downlink data transmittedon a certain downlink component carrier from retransmission controlsignal generating section 122, data transmission controlling section 106deletes the data kept in the manner described above and corresponding tothis downlink component carrier.

Modulation section 107 modulates the coded transmission data receivedfrom data transmission controlling section 106 and outputs the resultantmodulation signals to mapping section 108.

Mapping section 108 maps the modulation signals of the controlinformation received from modulation section 104 to the resource (PDCCH)indicated by the downlink control information assignment resourcereceived from control section 101 and outputs the resultant modulationsignals to IFFT section 109.

Mapping section 108 maps the modulation signals of the transmission datareceived from modulation section 107 to the resource (i.e., PDSCH (i.e.,downlink data channel)) indicated by the downlink data assignmentresource received from control section 101 (i.e., information includedin the control information) and outputs the resultant modulation signalsto IFFT section 109.

IFFT section 109 performs IFFT processing on the modulation signalsmapped in mapping section 108 and outputs the modulation signals to CPadding section 110. This causes the modulation signals to be transformedfrom frequency-domain to time-domain signals.

CP adding section 110 adds the same signal as that of the tail portionafter IFFT to the leading part thereof as a CP to form an OFDM signal,and outputs the OFDM signal to radio transmitting section 111.

Radio transmitting section 111 performs transmission processing such asD/A (digital to analog) conversion, amplification and up-conversion onthe OFDM signal, and transmits the OFDM signal to terminal 200 via anantenna.

Radio receiving section 112 receives uplink response signals orreference signals transmitted from terminal 200 via the antenna,performs reception processing such as down-conversion, A/D conversion onthe uplink response signals or reference signals, and outputs thesignals to CP removing section 113.

CP removing section 113 removes a CP added to the uplink responsesignals or reference signals after the reception processing and outputsthe signals to PUCCH extracting section 114.

PUCCH extracting section 114 extracts, from the PUCCH signals includedin the received signals, the signals in the PUCCH region correspondingto the bundled ACK/NACK resource previously indicated to terminal 200.Here, the bundled ACK/NACK resource is a PUCCH resource by which abundled ACK/NACK signal should be transmitted as described above and aresource that adopts a DFT-S-OFDM format configuration. Morespecifically, PUCCH extracting section 114 extracts the data part of thePUCCH region corresponding to the bundled ACK/NACK resource (i.e.,SC-FDMA symbols on which the bundled ACK/NACK resource is assigned) andthe reference signal part of the PUCCH region (i.e., SC-FDMA symbols onwhich the reference signals for demodulating the bundled ACK/NACKsignals are assigned). PUCCH extracting section 114 outputs theextracted data part to bundled A/N despreading section 119, and outputsthe reference signal part to despreading section 115-1.

PUCCH extracting section 114 extracts, from the PUCCH signals includedin the received signals, a plurality of PUCCH regions corresponding toA/N resources associated with CCEs occupied by PDCCH used fortransmission of downlink assignment control information (DCI), A/Nresources associated with eCCEs occupied by ePDCCH used for transmissionof downlink assignment control information (DCI) and a plurality of A/Nresources previously indicated to terminal 200. The A/N resource hereinrefers to the resource to be used for transmission of an A/N. Morespecifically, PUCCH extracting section 114 extracts the data part of thePUCCH region corresponding to the A/N resource (i.e., SC-FDMA symbols onwhich the uplink control signals are assigned) and the reference signalpart of the PUCCH region (i.e., SC-FDMA symbols on which the referencesignals for demodulating the uplink control signals are assigned). PUCCHextracting section 114 outputs both of the extracted data part andreference signal part to despreading section 115-2. In this manner, theresponse signals are received on the resource selected from the PUCCHresource associated with the CCE or eCCE and the specific PUCCH resourcepreviously indicated to terminal 200. Note that the method ofdetermining A/N resources (PUCCH resources to which response signals aremapped) will be described later.

Sequence controlling section 116 generates a base sequence that may beused for spreading each of the A/N indicated from terminal 200, thereference signals for the A/N, and the reference signals for the bundledACK/NACK signals (i.e., length-12 ZAC sequence). In addition, sequencecontrolling section 116 identifies a correlation window corresponding toa resource on which the reference signals may be assigned (hereinafter,referred to as “reference signal resource”) in PUCCH resources that maybe used by terminal 200. Sequence controlling section 116 outputs theinformation indicating the correlation window corresponding to thereference signal resource on which the reference signals may be assignedin bundled ACK/NACK resources and the base sequence to correlationprocessing section 117-1. Sequence controlling section 116 outputs theinformation indicating the correlation window corresponding to thereference signal resource and the base sequence to correlationprocessing section 117-1. In addition, sequence controlling section 116outputs the information indicating the correlation window correspondingto the A/N resources on which an A/N and the reference signals for theA/N are assigned and the base sequence to correlation processing section117-2.

Despreading section 115-1 and correlation processing section 117-1perform processing on the reference signals extracted from the PUCCHregion corresponding to the bundled ACK/NACK resource.

More specifically, despreading section 115-1 despreads the referencesignal part using a Walsh sequence to be used in secondary-spreading forthe reference signals of the bundled ACK/NACK resource by terminal 200,and outputs the despread signals to correlation processing section117-1.

Correlation processing section 117-1 uses the information indicating thecorrelation window corresponding to the reference signal resource andthe base sequence and thereby finds a correlation value between thesignals received from despreading section 115-1 and the base sequencethat may be used in primary-spreading in terminal 200. Correlationprocessing section 117-1 outputs the correlation value to bundled A/Ndetermining section 121.

Despreading section 115-2 and correlation processing section 117-2perform processing on the reference signals and A/Ns extracted from theplurality of PUCCH regions corresponding to the plurality of A/Nresources.

More specifically, despreading section 115-2 despreads the data part andreference signal part using a Walsh sequence and a DFT sequence to beused in secondary-spreading for the data part and reference signal partof each of the A/N resources by terminal 200, and outputs the despreadsignals to correlation processing section 117-2.

Correlation processing section 117-2 uses the information indicating thecorrelation window corresponding to each of the A/N resources and thebase sequence, and thereby finds a correlation value between the signalsreceived from despreading section 115-2 and a base sequence that may beused in primary-spreading by terminal 200. Correlation processingsection 117-2 outputs each correlation value to A/N determining section118.

A/N determining section 118 determines, on the basis of the plurality ofcorrelation values received from correlation processing section 117-2,which of the A/N resources is used to transmit the signals from terminal200, or if none of the A/N resources is used. When determining that thesignals are transmitted using one of the A/N resources from terminal200, A/N determining section 118 performs coherent detection using acomponent corresponding to the reference signals and a componentcorresponding to the A/N, and outputs the result of coherent detectionto retransmission control signal generating section 122. Meanwhile, whendetermining that terminal 200 uses none of the A/N resources, A/Ndetermining section 118 outputs the determination result indicating thatnone of the A/N resources is used to retransmission control signalgenerating section 122.

Bundled A/N despreading section 119 despreads, using a DFT sequence, thebundled ACK/NACK signals corresponding to the data part of the bundledACK/NACK resource received from PUCCH extracting section 114, andoutputs the despread signals to IDFT section 120.

IDFT section 120 transforms the bundled ACK/NACK signals in thefrequency-domain received from bundled A/N despreading section 119 intotime-domain signals by IDFT processing and outputs the bundled ACK/NACKsignals in the time-domain to bundled A/N determining section 121.

Bundled A/N determining section 121 demodulates the bundled ACK/NACKsignals corresponding to the data part of the bundled ACK/NACK resourcereceived from IDFT section 120, using the reference signal informationon the bundled ACK/NACK signals that is received from correlationprocessing section 117-1. In addition, bundled A/N determination section121 decodes the demodulated bundled ACK/NACK signals and outputs theresult of decoding to retransmission control signal generating section122 as the bundled A/N information. However, when the correlation valuereceived from correlation processing section 117-1 is smaller than athreshold, and bundled A/N determining section 121 thus determines thatterminal 200 does not use any bundled A/N resource to transmit thesignals, bundled A/N determining section 121 outputs the result ofdetermination to retransmission control signal generating section 122.

Retransmission control signal generating section 122 determines whetheror not to retransmit the data transmitted on the downlink componentcarrier (i.e., downlink data) on the basis of the information inputtedfrom bundled A/N determining section 121 and the information inputtedfrom A/N determining section 118 and generates retransmission controlsignals based on the result of determination. More specifically, whendetermining that downlink data transmitted on a certain downlinkcomponent carrier needs to be retransmitted, retransmission controlsignal generating section 122 generates retransmission control signalsindicating a retransmission command for the downlink data and outputsthe retransmission control signals to data transmission controllingsection 106. In addition, when determining that the downlink datatransmitted on a certain downlink component carrier does not need to beretransmitted, retransmission control signal generating section 122generates retransmission control signals indicating not to retransmitthe downlink data transmitted on the downlink component carrier andoutputs the retransmission control signals to data transmissioncontrolling section 106.

(Configuration of Terminal)

FIG. 10 is a block diagram illustrating a configuration of terminal 200according to Embodiment 1. In FIG. 10, terminal 200 includes radioreceiving section 201, CP removing section 202, fast Fourier transform(FFT) section 203, extraction section 204, demodulation section 205,decoding section 206, determination section 207, control section 208,demodulation section 209, decoding section 210, CRC section 211,response signal generating section 212, coding and modulation section213, primary-spreading sections 214-1 and 214-2, secondary-spreadingsections 215-1 and 215-2, DFT section 216, spreading section 217, IFFTsections 218-1, 218-2 and 218-3, CP adding sections 219-1, 219-2 and219-3, time-multiplexing section 220, selection section 221 and radiotransmitting section 222.

Radio receiving section 201 receives, via an antenna, an OFDM signaltransmitted from base station 100, performs reception processing such asdown-conversion, A/D conversion and/or the like on the received OFDMsignal and outputs the OFDM signal to CP removing section 202. It shouldbe noted that the received OFDM signal includes a PDSCH signal assignedto a resource in a PDSCH (i.e., downlink data), PDCCH signal assigned toa resource in a PDCCH signal or ePDCCH signal assigned to a resource inan ePDCCH.

CP removing section 202 removes a CP that has been added to the OFDMsignal from the OFDM signal that have undergone the reception processingand outputs the OFDM signal to FFT section 203.

FFT section 203 transforms the received OFDM signal from which the CPhas been removed into a frequency-domain signal by FFT processing andoutputs the resultant received signal to extraction section 204.

Extraction section 204 extracts, from the received signal to be receivedfrom FFT section 203, a downlink control channel signal (i.e., PDCCHsignal or ePDCCH signal) in accordance with coding rate information tobe received. That is, since the number of CCEs or eCCEs forming adownlink control information assignment resource varies depending on thecoding rate, extraction section 204 uses the number of CCEs or eCCEsthat corresponds to the coding rate as units of extraction processing,and extracts a downlink control channel signal and outputs the downlinkcontrol channel signal to demodulation section 205. Note that thedownlink control channel signal is extracted for each downlink componentcarrier.

Extraction section 204 extracts downlink data (i.e., downlink datachannel signal (i.e., PDSCH signal)) from the received signals on thebasis of information on the downlink data assignment resource intendedfor terminal 200 to be received from determination section 207 to bedescribed, hereinafter, and outputs the downlink data to demodulationsection 209. As described above, extraction section 204 receives thedownlink assignment control information (i.e., DCI) mapped to the PDCCHor ePDCCH and receives the downlink data on the PDSCH.

Demodulation section 205 demodulates the downlink control channel signalreceived from extraction section 204 and outputs the obtained result ofdemodulation to decoding section 206.

Decoding section 206 decodes the result of demodulation received fromdemodulation section 205 in accordance with the received coding rateinformation and outputs the obtained result of decoding to determinationsection 207.

Determination section 207 performs blind-determination (i.e.,monitoring) to find out whether or not the control information includedin the result of decoding received from decoding section 206 is thecontrol information intended for terminal 200. This determination ismade in units of decoding results corresponding to the units ofextraction processing. For example, determination section 207 demasksthe CRC bits by the terminal ID of terminal 200 and determines that thecontrol information resulted in CRC=OK (no error) as the controlinformation intended for terminal 200. Determination section 207 outputsinformation on the downlink data assignment resource intended forterminal 200, which is included in the control information intended forterminal 200, to extraction section 204.

In addition, when detecting the control information (i.e., downlinkassignment control information) intended for terminal 200, determinationsection 207 informs control section 208 that an ACK/NACK signal will begenerated (or is present). Moreover, when detecting the controlinformation intended for terminal 200 from a PDCCH signal or ePDCCHsignal, determination section 207 outputs information on a CCE that hasbeen occupied by the PDCCH or information on an eCCE that has beenoccupied by the ePDCCH to control section 208.

Control section 208 identifies the A/N resource associated with the CCEor the eCCE on the basis of the information on the CCE or the eCCEreceived from determination section 207. Control section 208 outputs theA/N resource associated with the CCE, the A/N resource associated withthe eCCE or base sequence and cyclic shift amount corresponding to theA/N resource indicated in advance from base station 100 toprimary-spreading section 214-1 and outputs a Walsh sequence and a DFTsequence corresponding to the A/N resource to secondary-spreadingsection 215-1. In addition, control section 208 outputs the frequencyresource information on the A/N resource to IFFT section 218-1. Notethat the method of determining A/N resources (PUCCH resources to whichresponse signals are mapped) will be described later.

When determining to transmit a bundled ACK/NACK signal using a bundledACK/NACK resource, control section 208 outputs the base sequence andcyclic shift value corresponding to the reference signal part (i.e.,reference signal resource) of the bundled ACK/NACK resource previouslyindicated by base station 100 to primary-despreading section 214-2 andoutputs a Walsh sequence to secondary-despreading section 215-2. Inaddition, control section 208 outputs the frequency resource informationon the bundled ACK/NACK resource to IFFT section 218-2.

Control section 208 outputs a DFT sequence used for spreading the datapart of the bundled ACK/NACK resource to spreading section 217 andoutputs the frequency resource information on the bundled ACK/NACKresource to IFFT section 218-3.

Control section 208 selects the bundled ACK/NACK resource or the A/Nresource and instructs selection section 221 to output the selectedresource to radio transmitting section 222. Moreover, control section208 instructs response signal generating section 212 to generate thebundled ACK/NACK signal or the ACK/NACK signal in accordance with theselected resource.

Demodulation section 209 demodulates the downlink data received fromextraction section 204 and outputs the demodulated downlink data todecoding section 210.

CRC section 211 performs error detection on the decoded downlink datareceived from decoding section 210, for each downlink component carrierusing CRC and outputs an ACK when CRC=OK (no error) or outputs a NACKwhen CRC=Not OK (error) to response signal generating section 212.Moreover, CRC section 211 outputs the decoded downlink data as thereceived data when CRC=OK (no error).

Response signal generating section 212 generates response signals on thebasis of the reception condition of downlink data (i.e., result of errordetection on downlink data) on each downlink component carrier inputtedfrom CRC section 211 and information indicating a predetermined groupnumber. More specifically, when instructed to generate the bundledACK/NACK signal from control section 208, response signal generatingsection 212 generates the bundled ACK/NACK signals including the resultsof error detection for the respective component carriers as individualpieces of data. Meanwhile, when instructed to generate ACK/NACK signalsfrom control section 208, response signal generating section 212generates an ACK/NACK signal of one symbol. Response signal generatingsection 212 outputs the generated response signal to coding andmodulation section 213.

Upon reception of the bundled ACK/NACK signal, coding and modulationsection 213 encodes and modulates the received bundled ACK/NACK signalto generate the modulation signal of 12 symbols and outputs themodulation signal to DFT section 216. In addition, upon reception of theACK/NACK signal of one symbol, coding and modulation section 213modulates the ACK/NACK signal and outputs the modulation signal toprimary-spreading section 214-1.

Primary-spreading sections 214-1 and 214-2 corresponding to the A/Nresources and reference signal resources of the bundled ACK/NACKresources spread the ACK/NACK signals or reference signals using thebase sequence corresponding to the resources in accordance with theinstruction from control section 208 and output the spread signals tosecondary-spreading sections 215-1 and 215-2.

Secondary-spreading sections 215-1 and 215-2 spread the receivedprimary-spread signals using a Walsh sequence or a DFT sequence inaccordance with an instruction from control section 208 and outputs thespread signals to IFFT sections 218-1 and 218-2.

DFT section 216 performs DFT processing on 12 time-series sets ofreceived bundled ACK/NACK signals to obtain 12 signal components in thefrequency-domain. DFT section 216 outputs the 12 signal components tospreading section 217.

Spreading section 217 spreads the 12 signal components received from DFTsection 216 using a DFT sequence indicated by control section 208 andoutputs the spread signal components to IFFT section 218-3.

IFFT sections 218-1, 218-2 and 218-3 perform IFFT processing on thereceived signals in association with the frequency positions where thesignals are to be allocated, in accordance with an instruction fromcontrol section 208. Accordingly, the signals inputted to IFFT sections218-1, 218-2 and 218-3 (i.e., ACK/NACK signals, the reference signals ofA/N resource, the reference signals of bundled ACK/NACK resource andbundled ACK/NACK signals) are transformed into time-domain signals.

CP adding sections 219-1, 219-2 and 219-3 add the same signals as thelast part of the signals obtained by IFFT processing to the beginning ofthe signals as a CP.

Time-multiplexing section 220 time-multiplexes the bundled ACK/NACKsignals received from CP adding section 219-3 (i.e., signals transmittedusing the data part of the bundled ACK/NACK resource) and the referencesignals of the bundled ACK/NACK resource to be received from CP addingsection 219-2 on the bundled ACK/NACK resource and outputs themultiplexed signals to selection section 221.

According to the instruction from control section 208, selection section221 selects one of the bundled ACK/NACK resource received fromtime-multiplexing section 220 and the A/N resource received from CPadding section 219-1 and outputs the signals assigned to the selectedresource to radio transmitting section 222.

Radio transmitting section 222 performs transmission processing such asD/A conversion, amplification and up-conversion on the signals receivedfrom selection section 221 and transmits the signals to base station 100from the antenna.

[Method of Determining ePDCCH-PUCCH R Resources]

Next, the method of determining ePDCCH-PUCCH resources in base station100 and terminal 200 configured as described above will be described.

FIG. 11 is a diagram provided for describing the method of determiningePDCCH-PUCCH resources according to the present embodiment. As shown inFIG. 11, ePDCCH-PUCCH resource region 300 is divided for each c′ andeach m and the resultant portions are arranged from the frequency enddirection to center direction of the component carrier in ascendingorder of m and in ascending order of c′.

In the present embodiment, base station 100 sets offset values (δ₁, δ₂,δ₃) for shifts made in a virtual PUCCH resource region corresponding tocurrent DL subframe m_(current).

Base station 100 first determines whether or not ePDCCH-PUCCH resource310 with offset value 0, that is, by implicit signaling collides with aPDCCH-PUCCH resource. In the case of no collision, base station 100indicates ARI=0 to terminal 200 so as to use ePDCCH-PUCCH resources 310.On the other hand, in the case of collision, base station 100sequentially determines collision or no collision in ePDCCH-PUCCHresources 311, 312 and 313 to which other offset values are added andindicates ARI corresponding to non-colliding ePDCCH-PUCCH resources toterminal 200.

Terminal 200 obtains c′ based on eCCE index n_(eCCE) and offset valueδ_(ARI) in a virtual PUCCH resource region corresponding to theindicated ARI and determines PUCCH resources to be used to indicateresponse signals indicating error detection results of downlink datafrom the PUCCH resource region corresponding to current DL subframem_(current).

[Effects]

Thus, according to the present embodiment, since a shift by an offsetvalue indicated by ARI is made only within PUCCH resources associatedwith m=m_(current), that is, the current DL subframe, no constraint isimposed on DL scheduling in future DL subframes.

Embodiment 2

In Embodiment 2, terminal 200 obtains c′ based on eCCE index n_(eCCE)and offset value δ_(ARI) corresponding to indicated ARI in a virtualPUCCH resource region which combines PUCCH resources corresponding tom=m_(current). Next, terminal 200 determines PUCCH resources to be usedto indicate response signals indicating error detection results ofdownlink data in an ePDCCH-PUCCH resource region which is actually used.

FIG. 12 is a diagram provided for describing a method of determiningePDCCH-PUCCH resources according to the present embodiment. In theexample in FIG. 12, suppose m_(current)=2. In FIG. 12, PUCCH resourceregion 350 is a virtual PUCCH resource region combining PUCCH resourceswith m=m_(current)=2. PUCCH resource region 350 is divided for each c′and resultant portions are arranged from the frequency end direction tocenter direction of a component carrier in ascending order of c′.

Base station 100 calculates c′ to which n_(eCCE)+δ_(ARI) belongs invirtual PUCCH resource region 350 according to equation 6. Base station100 determines one of PUCCH resources (360, 361, 362, 363) based on thecalculated c′ according to equation 7.[6]N _(c′) ≤n _(eCCE)+δ_(ARI) <N _(c′+1)  (Equation 6)[7]n _(PUCCH,j) ⁽¹⁾=(M−m−1)·N _(c′) +m·N _(c′+1) +n _(eCCE,m)+δ_(ARI) +N_(PUCCH) ⁽¹⁾′  (Equation 7)

In equation 6, c′ need not always be the same value as c or within arange of the same value in PDCCH-PUCCH. In equation 7, N⁽¹⁾ _(PUCCH)′ isan offset value corresponding to all ePDCCH-PUCCH resources previouslyset in terminal 200, but may also be a value different from offset valueN⁽¹⁾ _(PUCCH) corresponding to all PDCCH-PUCCH resources.

As described above, in a special subframe in which the number of OFDMsymbols used for the downlink is small, the size of an ePDCCH searchspace set is half the size of a normal subframe. Thus, while an offsetvalue for a normal subframe is δ, an offset value for a special subframemay be δ/2.

[Effects]

Thus, according to the present embodiment, a shift by an offset valueindicated by ARI is made in a virtual PUCCH resource region.Furthermore, for a virtual PUCCH resource, only a PUCCH resourceassociated with m=m_(current), that is, a current DL subframe is used,and no constraint is imposed on DL scheduling in future DL subframes.Even an offset value of a small absolute value can indicate anePDCCH-PUCCH resource corresponding to the same m and different c′, andtherefore when a positive offset value is given, it is possible to makea shift to an ePDCCH-PUCCH resource region having a lower probability ofcollision with PDCCH-PUCCH resources. Furthermore, these effects can beobtained even when the same offset value is set with different c′ and m.

In FIG. 12, the virtual PUCCH resource region includes, except theePDCCH-PUCCH resource region corresponding to m=2, resources outside theePDCCH-PUCCH resource region (e.g., PUSCH region). The presentembodiment may operate PUCCH resources shifted by an offset so as to beable to (1) indicate resources outside the ePDCCH-PUCCH resource regionor (2) always indicate only resources inside the ePDCCH-PUCCH resourceregion.

Hereinafter, (1) a case where PUCCH resources are not limited to withinthe ePDCCH-PUCCH resource region and (2) a case where PUCCH resourcesare limited to within the ePDCCH-PUCCH resource region will bedescribed.

(Variation 1)

Variation 1 is (1) a case where PUCCH resources are not limited towithin the ePDCCH-PUCCH resource region.

FIG. 13 and FIG. 14 illustrate an operation method when the virtualPUCCH resource region is not limited to within the ePDCCH-PUCCH resourceregion.

In the operation method shown in FIG. 13, resources outside theePDCCH-PUCCH resource region are also divided for each c′ and each m(that is, according to the same rule as that of ePDCCH-PUCCH) in actualePDCCH-PUCCH resource region 300. In FIG. 13, an ePDCCH-PUCCH resourceregion is defined by c′=0, 1, 2, 3 and resources outside theePDCCH-PUCCH resource region (e.g., PUSCH region) are defined by c′=4, .. . . In virtual PUCCH resource region 350, PUCCH resources are shiftedbased on offset values indicated by ARI in the ePDCCH-PUCCH resourceregion when m=m_(current) and in the resource region outside theePDCCH-PUCCH resource region. Note that equation 6 and equation 7 followthe present operation method.

On the other hand, in the operation method shown in FIG. 14, in actualePDCCH-PUCCH resource region 300, resources outside the ePDCCH-PUCCHresource region are not divided for each c′ and each m. In the virtualPUCCH resource region, resources outside the ePDCCH-PUCCH resourceregion in addition to the ePDCCH-PUCCH resource region whenm=m_(current) are added in the same way as in the actual resourceregion. In this resource region, PUCCH resources are shifted based onoffset values indicated by ARI. In the present operation method, when c′that satisfies equation 6 is a maximum value of c′ defined as theePDCCH-PUCCH resource region (defined as c′_(max)) (c′_(max)=3 in theexample of FIG. 14) or below, PUCCH resources are calculated accordingto equation 6 and equation 7, and when c′ is greater than the maximumvalue of c′ defined as the ePDCCH-PUCCH resource region, PUCCH resourcesare calculated according to equation 8.[8]n _(PUCCH,j) ⁽¹⁾=(M−1)·N _(c′) _(max) ₊₁+(n _(eCCE,m)+δ_(ARI) −N _(c′)_(max) ₊₁)+N _(PUCCH) ⁽¹⁾′  (Equation 8)

In the operation method shown in FIG. 13 above, since the resourceregion outside the ePDCCH-PUCCH resource region is divided for each m,no collision of PUCCH resources indicated by ePDCCH occurs betweendifferent m's even outside the ePDCCH-PUCCH resource region. Therefore,this operation method is useful when the ePDCCH-PUCCH resource region issmall, when the absolute value of an offset value is large or the like,that is, when many shift destinations by an offset go out of theePDCCH-PUCCH resource region.

On the other hand, in the operation method shown in FIG. 14 above, theresource region outside the ePDCCH-PUCCH resource region is not dividedfor each m. For this reason, this operation method is useful when theePDCCH-PUCCH resource region is large, when the absolute value of anoffset value is small or the like, that is, when many shift destinationsby an offset are included in the ePDCCH-PUCCH resource region.

(Variation 2)

Variation 2 corresponds to (2) a case where PUCCH resources are limitedto within the ePDCCH-PUCCH resource region.

FIG. 15 illustrates an operation method when PUCCH resources in avirtual PUCCH resource region are limited to within the ePDCCH-PUCCHresource region.

In the operation method (method 1) shown in FIG. 15, an ePDCCH-PUCCHresource region in the virtual PUCCH resource region when m=m_(current)is rotated. In this rotating resource region, PUCCH resources areshifted based on an offset value indicated by ARI. In the presentoperation method, the entire virtual PUCCH resource region is rotated sothat c′ that satisfies equation 9 becomes a maximum value of c′ orbelow, c′ being defined as the ePDCCH-PUCCH resource region (defined asc′_(max)) (c′_(max)=3 in the example of FIG. 15). PUCCH resources arecalculated from c′ obtained according to equation 10.[9]N _(c′)≤(n _(eCCE)+δ_(ARI))mod N _(c′) _(max) ₊₁ <N _(c′+1)  (Equation9)[10]n _(PUCCH,j) ⁽¹⁾=(M−m−1)·N _(c′) +m·N _(c′+1)+(n _(eCCE,m)+δ_(ARI))mod N_(c′) _(max) ₊₁ +N _(PUCCH) ⁽¹⁾′  (Equation 10)

In method 1 shown in FIG. 15, c′ having a high occupancy of PDCCH-PUCCHis returned to the ePDCCH-PUCCH resource region due to the rotation ofthe entire virtual PUCCH resource region (at the time of δ₃ shift inFIG. 15). Since the ePDCCH-PUCCH resources which are shift destinationsare more likely to have been occupied by PDCCH-PUCCH resources, there isa high possibility that the shift destinations may not be used. Thus, asshown in method 2 or method shown in FIG. 15, a rotation or loopbackmethod may be used so that greater c′ is used preferentially. Morespecifically, according to method 2, rotation is made within theePDCCH-PUCCH resource region corresponding to c′ greater than apredetermined threshold (2<c′ in FIG. 15). According to method 3, aloopback is made (a negative offset value is used) after a lowest end ofthe ePDCCH-PUCCH resource region corresponding to a maximum value of c′defined as the ePDCCH-PUCCH resource region (direction toward the centerof the component carrier is defined as down).

(Variation 3)

The present embodiment has been described based on a positive offsetvalue which is a direction in which c′ and m increase as a premise, butthe present invention is not limited to this, and a negative offsetvalue may be used and PUCCH resources closer to the end of the componentcarrier may be used as well. For PUCCH, frequency hopping is performedsymmetrically with respect to the center frequency of each componentcarrier for each slot, and therefore the possibility that resourcesoutside the system band may be used increases by positively using anegative offset value, and a large frequency diversity effect is therebyobtained. However, the smaller the value of c′, the higher theprobability that ePDCCH-PUCCH resources will collide with PDCCH-PUCCHresources becomes. For that reason, for example, as shown in FIG. 16, anoperation may be adopted such that collision is avoided using a positiveoffset for c′ smaller than a predetermined threshold (e.g., 1.5) and afrequency diversity effect is increased using a negative offset for c′greater than the predetermined threshold. That is, in the presentembodiment, the offset value can take any one of positive and negativevalues. The present embodiment does not limit all c′ and m values to thesame offset value.

(Variation 4)

As described above, c′ in ePDCCH-PUCCH resources need not always havethe same value and the same range of values as those of PDCCH-PUCCH.FIG. 17 and FIG. 18 illustrate a case where the present embodiment isapplied when c′={0}. FIG. 17 illustrates an example of a case where theePDCCH-PUCCH resource region is shared with the PDCCH-PUCCH resourceregion corresponding to c=1. FIG. 18 illustrates an example of a casewhere the ePDCCH-PUCCH resource region is not shared with thePDCCH-PUCCH resource region.

As shown in FIG. 17, when the ePDCCH-PUCCH resource region is sharedwith the PDCCH-PUCCH resource region, the scale of the PUCCH resourceregion for each c and each m is equalized to the scale of the PUCCHresource region for each c′ and each m between the shared PDCCH-PUCCHresource region (c=1) and ePDCCH-PUCCH resource region (c′=0). That is,in FIG. 17, the PDCCH-PUCCH resource region for each m when c=1 and theePDCCH-PUCCH resource region for each m when c′=0 have the same scale.By this means, since PDCCH-PUCCH and ePDCCH-PUCCH can use a PUCCH regioncorresponding to the same m with an actual PUCCH resource number, theone control channel (PDCCH or ePDCCH) in a current DL subframe will notimpose constraints on scheduling of the other control channel (ePDCCH orPDCCH) in future DL subframes.

As described above, the scale of the PDCCH region is defined by CFI(Control Format Indicator). Therefore, the maximum value that cindicating the scale of the PDCCH-PUCCH resource region can take dependson the magnitude of CFI.

CFI is intended to indicate the scale of the PDCCH region. Therefore, ifthe OFDM symbol from which assignment of ePDCCH (and PDSCH) is startedis assigned from a fixed OFDM symbol (or OFDM symbol preset by basestation 100) independent of the scale of the PDCCH region, terminal 200that receives ePDCCH but does not receive PDCCH need not receive CFI.That is, terminal 200 that receives ePDCCH but does not receive PDCCHmay be operated assuming that without receiving CFI, for example, CFI=3(that is, the PDCCH region occupies the first to third OFDM symbols) isfixedly set and assignment of ePDCCH starts from the fourth OFDM symbol.However, in this case, terminal 200 does not know the scale of theactual PDCCH region. Thus, terminal 200 does not know the maximum valuethat c can take either. In such a case, terminal 200 may calculate themaximum value that c can take assuming CFI=3 which is the value assumedabove. Base station 100 may preset the maximum value that c can take orinformation pursuant thereto (e.g., CFI value) in terminal 200.

As shown in FIG. 18, when not shared with the PDCCH-PUCCH resourceregion, the design of the ePDCCH-PUCCH resource region is notconstrained by the design of the PDCCH-PUCCH resource region. For thatreason, the method of calculating the scale of the ePDCCH-PUCCH resourceregion for each c′ and each m is not constrained by the method(N_(c+1)−N_(c)) of calculating the scale of the PDCCH-PUCCH resourceregion for each c and each m. The present embodiment may adopt anoperation such that the ePDCCH-PUCCH resource region overlaps with thePDCCH-PUCCH resource region (e.g., δ₃ in FIG. 18) by a shift based onthe offset value indicated by ARI. Alternatively, the present embodimentmay also adopt an operation such that the resources are arranged outsidethe PDCCH-PUCCH resource region and outside the ePDCCH-PUCCH resourceregion (e.g., δ₁ and δ₂ in FIG. 18). If an operation is positivelyadopted such that the ePDCCH-PUCCH resource region overlaps with thePDCCH-PUCCH resource region, it is possible to reduce the overhead oftotal PUCCH resources.

(Variation 5)

A case has been described in the present embodiment where an eCCE indexis used as an implicit parameter, but the present invention is notlimited to this. In addition to the eCCE index, the implicit parametermay also be an index of resource element group (REG) eREG in the ePDCCHregion, PRB (Physical Resource Block) number of PDSCH or antenna portnumber with which ePDCCH is indicated. A plurality of ePDCCH searchspace sets may be defined, and which search space set is used toindicate ePDCCH can also be said to be an implicit parameter. Some ofthese parameters or a combination of these parameters are also implicitparameters. In short, when DL assignment and PDSCH are assigned toterminal 200, the implicit parameter can be any parameter that is atleast implicitly determined.

(Variation 6)

Furthermore, the present invention is not necessarily applied to onlythe method of indicating PUCCH resources based on an implicit parameterand an offset value (relative value) from the implicit parameterindicated by ARI, and as shown in FIG. 19, terminal 200 may also obtainc′ based on an “explicit resource (absolute value) in a virtual PUCCHresource region” indicated by ARI in the virtual PUCCH resource regioncorresponding to m=m_(current) and then identify a PUCCH resource in theactual PUCCH resource region. In this case, as shown in FIG. 19, evenwhen the explicit resources (absolute values) in the virtual PUCCHresource region are the same between different m's, those fitting toeach m are used in the actual PUCCH resource region. Note that the“explicit resource (absolute value) in the virtual PUCCH resourceregion” may also be expressed as an “offset value (absolute value) froma fixed position (e.g., frequency end of a component carrier) in thevirtual PUCCH resource region.”

That is, when ARI indicates the “explicit resource (absolute value) inthe virtual PUCCH resource region,” an ePDCCH-PUCCH resourcecorresponding to m=m_(current) is indicated within the PDCCH-PUCCHresource region or within the ePDCCH-PUCCH resource region, which willimpose no scheduling constraint in future DL subframes.

(Variation 7)

A shift by an offset value is made in the virtual PUCCH resource regionin the above description, and the following description will show that ashift by an offset can be realized without imposing any constraint on DLscheduling in future DL subframes by imposing constraints on the methodof dividing the PUCCH resource region for each c′ and each m, and anoffset value. However, the following is not intended to avoid collisionbetween PDCCH-PUCCH resources and ePDCCH-PUCCH resources but collisionbetween ePDCCH-PUCCH resources.

According to the present variation, base station 100 sets differentePDCCH search space sets between terminals. In this case, the scale (Nin FIG. 23) of the PUCCH resource region for each c′ and each m is setto a fixed value irrespective of the ePDCCH search space. However, inspecial subframes in which the number of OFDM symbols used for thedownlink is small, the scale of the PUCCH resource region for each c′and each m may be set to N/2. According to FIG. 23, suppose ePDCCHsearch space set A having a scale of N_(eCCE) (=N) and ePDCCH searchspace set B having a scale of N_(eCCE)′ (=2N) are set, and leading eCCEindices n_(eCCE) and n_(eCCE)′ to which DL assignment is assigned in therespective ePDCCH search spaces indicate the same PUCCH resource. Inthis case, since collision between PUCCH resources occurs, it ispossible to avoid collision by adding an offset having at least a scaleof N_(eCCE) or N_(eCCE)′ or more of the ePDCCH search space set to theone PUCCH resource. However, it is not desirable to impose schedulingconstraints in future DL subframes as described above.

Thus, in the present variation, as shown in FIG. 24, offset value δ isassumed to be MN for ePDCCH search space set A having a scale ofN_(eCCE)=N in a physical PUCCH resource region. Here, N is the scale ofa PUCCH resource region for each c′ and each m common among differentsearch space sets. By setting scale N of the PUCCH resource region foreach c′ and each m to a fixed value irrespective of the ePDCCH searchspace, it is possible to avoid collision between ePDCCH-PUCCH resourcesalso in the physical PUCCH resource region without imposing constraintson future scheduling.

In order to avoid collision between PUCCH resources in FIG. 23, terminal200 having ePDCCH search space set B of N_(eCCE)′=2N in scale as shownin FIG. 25 may make a shift by an offset. In this case, offset value δis assumed to be 2MN. This can avoid collision between ePDCCH-PUCCHresources without imposing constraints on future scheduling.

In the example of FIG. 25, although it is possible to avoid collision ofPUCCH resources by setting offset value δ to MN, a shift by offset valueδ=MN may be made by another terminal having ePDCCH search space set A ofN_(eCCE)=N in scale. Therefore, the shift by offset may be determinedbased on the scale of the ePDCCH search space whereby DL assignmentintended for the terminal is indicated. An example of N_(eCCE)=N andN_(eCCE)′=2N has been shown above, and generally, the value of offset δmay be MN in a range of N_(eCCE)≤N and the value of offset δ may be 2MNin a range of N<N_(eCCE)≤2N. When these are expressed in a generalizedmanner, offset value δ (δ_(ARI)) may be set as shown in equation 11.Here, N_(eCCE) represents the scale of the ePDCCH search space setwhereby DL assignment is indicated in terminal 200 that makes a shift byoffset. M represents a bundling window.[11]δ_(ARI) =┌N _(eCCE) /N┐·M·N  (Equation 11)

As described above, the scale of the ePDCCH search space set in aspecial subframe in which the number of OFDM symbols used for thedownlink is small is half the scale of a normal subframe. Thus, whilescale N_(Normal) of the PUCCH resource region for each c′ and each m fora normal subframe is set to N, scale N_(Special) of the PUCCH resourceregion for each c′ and each m for a special subframe may be set to N/2.At this time, the offset value in FIG. 23 according to the descriptionof the present variation is (3+1/2)N when bundling window M includes aspecial subframe in which the number of OFDM symbols used for thedownlink is small and is 4N when bundling window M does not include anyspecial subframe in which the number of OFDM symbols used for thedownlink is small. The offset value in FIG. 24 is 2×(3+1/2)N whenbundling window M includes a special subframe in which the number ofOFDM symbols used for the downlink is small and is 2×4N when bundlingwindow M does not include any special subframe in which the number ofOFDM symbols used for the downlink is small. That is, the offset valueat this time is as shown in equation 12 when bundling window M includesa special subframe in which the number of OFDM symbols used for thedownlink is small and as shown in equation 13 when bundling window Mdoes not include any special subframe in which the number of OFDMsymbols used for the downlink is small.[12]δ_(ARI) =┌N _(eCCE,m) /N┐·((M−1)·N _(Normal) +N _(Special))  (Equation12)[13]δ_(ARI) =┌N _(eCCE,m) /N┐·M·N _(Normal)  (Equation 13)

Although the present invention relates to TDD, if the present inventionis applied to FDD, M=1 is assumed and the PUCCH resource region for eachc′ and each m need not be considered, and therefore N need not beconsidered. That is, offset value δ (δ_(ARI)) is the scale of the ePDCCHsearch space set to which DL assignment intended for the terminal isassigned in terminal 200 as shown in equation 14.[14]δ_(ARI) =N _(eCCE)  (Equation 14)

Since the scale of the ePDCCH search space set is an even numberirrespective of FDD or TDD and the aggregation level of ePDCCH is aneven number except 1, PUCCH resources corresponding to even-numberedeCCE indices are likely to be occupied. Based on this, when the offsetvalue shown in equation 11 and equation 14 is an even number, an offsetvalue obtained by adding +1 or −1 to the offset value may be used.

Based on the above description, the method of determining PUCCHresources according to the present variation will be described usingequations.

Terminal 200 calculates c′ to which leading eCCE index n_(eCCE) belongsaccording to equation 15, DL assignment intended for the terminal beingassigned to leading eCCE index n_(eCCE). Terminal 200 determines PUCCHresources according to equation 16 based on the calculated c′.[15]c′·N≤n _(eCCE)<(c′+1)·N  (Equation 15)[16]n _(PUCCH,j) ⁽¹⁾=(M−m−1)·c′N+m·(c′+1)N+n _(eCCE,m) +N _(PUCCH)⁽¹⁾′  (Equation 16)

N⁽¹⁾ _(PUCCH)′ is an offset value preset in terminal 200 for allePDCCH-PUCCH resources and may also take a value which varies from oneePDCCH search space set to another.

When a PUCCH resource determined according to equation 16 collides witha PUCCH resource used by another terminal, base station 100 may instructterminal 200 to make a shift of the PUCCH resource by dynamic offsetδ_(ARI) using ARI indicated by DL assignment intended for terminal 200.At this time, terminal 200 determines a PUCCH resource after the shiftusing equation 17. The value of c′ in equation 17 is the same as thevalue of equation 16. The value of δ_(ARI) in equation 17 is determinedaccording to equation 11.[17]n _(PUCCH,j) ⁽¹⁾=(M−m−1)·c′N+m·(c′+1)N+n _(eCCE,m)+δ_(ARI) +N _(PUCCH)⁽¹⁾′  (Equation 17)

[Effect by Setting N to Fixed Value]

Here, the effect of setting scale N of the PUCCH resource region foreach c′ and each m to a fixed value irrespective of the ePDCCH searchspace will be described with reference to FIG. 26, FIG. 27 and FIG. 28.

When base station 100 sets different ePDCCH search space sets (set A andset B) between terminals, the following two methods can be considered asoperation methods available to base station 100.

(1) Scheduled to only one ePDCCH search space set

(2) Simultaneously scheduled (in the same subframe) to both ePDCCHsearch space sets

(1) When scheduled to only one ePDCCH search space set, PUCCH resourcesas shown in FIG. 26 are shared to reduce the overhead of PUCCH resourcescorresponding to each ePDCCH search space set. Here, FIG. 26 illustratesindication of assignment of downlink data by ePDCCH and a correspondingPUCCH resource in subframe #5 of UL-DL Configuration #2 shown in FIG. 3.In FIG. 26, only ePDCCH search space set A is scheduled. Although thesame PUCCH resource region as that of ePDCCH search space set A isassociated with ePDCCH search space set B, no collision of PUCCHresources occurs between both sets because ePDCCH search space set B isnot scheduled.

On the other hand, (2) when both ePDCCH search space sets aresimultaneously scheduled, collision of PUCCH resources occurs betweenboth sets, and it is therefore preferable not to share the PUCCHresource region.

Here, a case will be considered where the base station performsoperation by dynamically switching between the two operation methodsabove, that is, (1) only one ePDCCH search space set is scheduled and(2) both ePDCCH search space sets are simultaneously (in the samesubframe) scheduled. At this time, when PUCCH resources are sharedbetween the sets, overhead of the PUCCH resources can be reduced, but onthe other hand, collision of PUCCH resources occurs between the sets. Inorder to avoid collision, an offset value greater than the scale of theePDCCH search space set needs to be used, and the value is 4, 8, 16, 32or the like as described above, that is, greater than 1.

For this reason, even when different ePDCCH search space sets are setbetween the terminals, the possibility that the offset destination PUCCHresource will become m>m_(current) when m corresponding to a DL subframeat certain timing is assumed to be m_(current) becomes higher than thecase with “+1” which is the offset value applied in the PDCCH-PUCCHresource region. Therefore, when downlink data assignment is indicatedby ePDCCH, constraints are imposed on scheduling for future DLsubframes. The constraints become bigger as the value of m increases.Therefore, the base station is more likely not to be able to assigncontrol information to an optimum terminal. Moreover, the base stationrequires scheduling taking into account a relationship between subframesand the base station scheduler becomes more complicated.

As described above, the base station may set different ePDCCH searchspace sets between terminals and these ePDCCH search space sets may bedifferent in scale. In addition, the base station can set differentstart positions N⁽¹⁾ _(PUCCH) of PUCCH resources for the respectiveePDCCH search space sets. FIG. 27 illustrates PUCCH resources when thescale of ePDCCH search space set A is N_(eCCE), the corresponding startposition of the PUCCH resource is N⁽¹⁾ _(PUCCH), the scale of ePDCCHsearch space set B is N_(eCCE)′ (≠N_(eCCE)) and the corresponding startposition of the PUCCH resource is N⁽¹⁾ _(PUCCH)′. Here, in FIG. 27,PUCCH resources for ePDCCH are calculated based on equation 1, equation2 and equation 3 as in the case of PUCCH resources for PDCCH. ScalesN¹⁻⁰, N²⁻¹ and N³⁻² of the PUCCH resource region for each c and each mare calculated by N₁−N₀, N₂−N₁ and N₃−N₂ using equation 2 and thesescales take different values. That is, the scale of the PUCCH resourceregion for each c and each m varies for each c. As shown in FIG. 27,when start position N⁽¹⁾ _(PUCCH) of PUCCH of ePDCCH search space set Acoincides with the start of c=1 of the PUCCH resource of ePDCCH searchspace set B, the PUCCH resource corresponding to m=0 of ePDCCH searchspace set A coincides with the PUCCH resource corresponding to m=0 ofePDCCH search space set B, but the leading part of the PUCCH resourcecorresponding to m=1 of ePDCCH search space set A coincides with thePUCCH resource corresponding to m=0 of ePDCCH search space set B (shadedpart (A) in FIG. 27). At this time, when m=0 of ePDCCH search space setB, if the PUCCH resource of shaded part (A) in FIG. 27 is used, ePDCCHsearch space set A cannot use the PUCCH resource when m=1 which is afuture subframe for m=0. The same applies to shaded parts (B) and (C) inFIG. 27. Therefore, when the scale of the ePDCCH search space and thestart position of a PUCCH corresponding to the ePDCCH search space aredifferent among a plurality of ePDCCH search spaces, constraints arealso imposed on scheduling for future DL subframes.

Thus, as shown in FIG. 28, by dividing the PUCCH regions for ePDCCHsearch space set A and ePDCCH search space set B by the same scale Nrespectively, the same value of m is always associated by PUCCHresources between the sets, and it is thereby possible to avoidconstraints on future scheduling due to the difference in scale of theePDCCH search space as shown in FIG. 27.

The effect of setting scale N of the PUCCH resource region for each c′and each m to a fixed value irrespective of the ePDCCH search space hasbeen described so far.

[Value of N]

N according to the present variation needs only to have a common scalewhen a PUCCH resource region is shared among a plurality of ePDCCHsearch space sets, and a more specific example of the setting method ofN is shown below though this does not necessarily limit the value orrange of values thereof. Note that when the PUCCH resource region isshared among a plurality of ePDCCH search space sets, the value of Nneeds to have a scale common among the plurality of ePDCCH search spacesets as described above, but if the PUCCH resource region is not sharedamong the plurality of ePDCCH search space sets, the value of N may havea scale common among a plurality of ePDCCH search space sets or thevalue of N may have a different scale.

(Method 1)

FIG. 29 illustrates a specific example of a case where a PUCCH resourceregion is shared among a plurality of ePDCCH search space sets,N_(eCCE)=8 as the scale of ePDCCH search space set A, N_(eCCE)=32 as thescale of ePDCCH search space set B and N=32 as the scale of N. When thePUCCH resource region is assigned to only ePDCCH search space set A,corresponding PUCCH resources are 8 PUCCH resources (shaded parts inFIG. 29) of each PUCCH resource region for each m and each c′ of N=32and the remaining 24 resources are not used as the PUCCH resourcescorresponding to search space set A. Since PUCCH resources used aredispersed within the PUCCH resource region, when the PUCCH resourceregion is shared among a plurality of ePDCCH search space sets, if thePUCCH resource region is assigned to only ePDCCH search space set A, itis obvious that setting N=32 causes overhead of PUCCH to increase.

Next, FIG. 30 illustrates a specific example of a case where N=32 inFIG. 29 is changed to N=8. When the PUCCH resource region is assigned toonly ePDCCH search space set A, the corresponding PUCCH resources(shaded parts in FIG. 30) are arranged tightly close to each otherwithin the PUCCH resource region. Thus, when the PUCCH resource regionis shared among a plurality of ePDCCH search space sets, if the PUCCHresource region is assigned to only ePDCCH search space set A, settingN=8 makes it possible to reduce the overhead of PUCCH compared tosetting N=32.

As described above, the scale of each ePDCCH search space set is 4, 8,16, 32 or the like. Furthermore, the value of N is preferably divisibleamong a plurality of ePDCCH search space sets because PUCCH resourcesare never dispersed and PUCCH resources can be efficiently used in thisway. As such, when the PUCCH resource region is shared among a pluralityof ePDCCH search space sets of different scales, the value of N may beset to a smaller ePDCCH search space set. That is, as shown in FIG. 29and FIG. 30, when the scale of ePDCCH search space set A is N_(eCCE)=8and the scale of ePDCCH search space set B is N_(eCCE)′=32, N=8 is set.However, since terminal 200 does not recognize any ePDCCH search spaceother than ePDCCH search space sets intended for the terminal, it is thepremise that the scales of ePDCCH search space set A and ePDCCH searchspace set B should be indicated to terminal 200.

When the PUCCH resource region is shared among a plurality of ePDCCHsearch space sets of different scales, overhead of PUCCH can be reducedby setting the value of N to a smaller ePDCCH search space set.

From the above, the method of determining N in terminal 200 according tomethod 1 is as follows.

When PUCCH resources are shared among a plurality of ePDCCH search spacesets set in terminal 200, terminal 200 sets as the value of N, the scaleof the smallest ePDCCH search space among the plurality of ePDCCH searchspace sets set in the terminal among which the PUCCH resources areshared. This can reduce the overhead of PUCCH.

Here, the decision as to whether or not to share PUCCH resources isdetermined as follows. When it is assumed that the start positions ofPUCCH resources relating to ePDCCH search space set A and ePDCCH searchspace set B set in terminal 200 are N⁽¹⁾ _(PUCCH) and N⁽¹⁾ _(PUCCH)′(N⁽¹⁾ _(PUCCH)≤N⁽¹⁾ _(PUCCH)′) respectively, and when equation 18 issatisfied regarding scale N_(eCCE) of ePDCCH search space set A, ePDCCHsearch space set A and ePDCCH search space set B share the PUCCHresources. The PUCCH resources are not shared when equation 18 is notsatisfied.[18]N _(PUCCH) ⁽¹⁾ +M·N _(eCCE) >N _(PUCCH) ⁽¹⁾′  (Equation 18)

When the PUCCH resource region is not shared among a plurality of ePDCCHsearch space sets set in terminal 200, the scale of ePDCCH search spacesets may be set to the value of N for the ePDCCH search space sets.Alternatively, the scale of ePDCCH search space sets may be set to thesmallest among the scales of ePDCCH search space sets set in terminal200 for simplicity.

To put it more simply, even when the scale of ePDCCH search space setswhich becomes the smallest among all ePDCCH search space sets set interminal 200 is set to the value of N, it is likewise possible to reducethe overhead of PUCCH.

(Method 2)

FIG. 31 illustrates a PUCCH resource region when N=4. PUCCHs can bemultiplexed with one PRB (Physical Resource Block) by a maximum of 36PUCCHs/Δ_(PUCCH_OFFSET) in ascending order of PUCCH resource indices.Here, Δ_(PUCCH_OFFSET) represents the amount of offset of PUCCHs mappedwithin one PRB and is generally Δ_(PUCCH_OFFSET)=2 or 3. That is, whenΔ_(PUCCH_OFFSET)=2, 3, a maximum 18 and 12 PUCCHs can be multiplexedwith one PRB. However, in reality, interference between PUCCHs withinthe PRB increases as the multiplexing number increases, and thereforethe number of PUCCHs that can be multiplexed with one PRB is smallerthan the maximum multiplexing number. As shown in the shaded part inFIG. 31, PUCCHs corresponding to m=0, 1, 2, 3 (4 m's) are multiplexedwith one PRB when N=4 (note that Δ_(PUCCH_OFFSET)=2 in FIG. 31). As thevalue of m increases, the number of PUCCHs arranged in the PRB increasesand interference increases correspondingly. Thus, the greater the valueof m, the fewer PUCCHs can be arranged in the PRB. This imposesconstraints on scheduling for future subframes.

When the PUCCH resource region is shared among a plurality of ePDCCHsearch space sets in different scales, setting the value of N to thelarger of the ePDCCH search space sets makes it possible to reduceconstraints on scheduling for future subframes due to the multiplexingof PUCCHs with many DL subframes within one PRB.

From the above, the method of determining N in terminal 200 according tomethod 2 is as follows.

When PUCCH resources are shared among a plurality of ePDCCH search spacesets set in terminal 200, terminal 200 sets as the value of N, the scaleof the largest ePDCCH search space among the plurality of ePDCCH searchspace sets set in the terminal among which the PUCCH resources areshared. This can reduce constraints on scheduling for future subframesdue to the multiplexing of PUCCHs with many DL subframes within one PRB.

Here, the decision as to whether or not to share PUCCH resources isdetermined according to equation 18 as in the case of method 1.

When method 2 is applied, since the scale of the largest ePDCCH searchspace among a plurality of ePDCCH search space sets set in the terminalis assumed to be the value of N, the value of c′ is always 0. That is,parameter c′ need not be taken into account in this case.

Note that when PUCCH resources are not shared among a plurality ofePDCCH search space sets set in terminal 200, the scales of the ePDCCHsearch space sets may be set to the value of N for the respective ePDCCHsearch space sets. Alternatively, the scales of ePDCCH search space setsmay be set to the largest among the scales of ePDCCH search space setsset in terminal 200 for simplicity.

To put it more simply, even when the scale of an ePDCCH search space setwhich becomes the largest among all ePDCCH search space sets set interminal 200 is set to the value of N, it is likewise possible to reduceconstraints on scheduling for future subframes due to the multiplexingof PUCCHs with many DL subframes within one PRB.

(Method 3)

Method 1 and method 2 are in a trade-off relationship and the degree ofimportance to be attached to effects obtained from method 1 and method 2varies depending on how the system that applies the present variation isoperated. In a system that attaches importance to downlinkcommunication, a UL-DL configuration having a high DL subframe ratiosuch as UL-DL Configuration 2 is used. In this case, method 1 that canreduce the overhead of PUCCH is effective since it is necessary toindicate HARQ-ACK for downlink data in a plurality of DL subframescollectively in one UL subframe. Method 2 is effective when attachingimportance to a simpler base station configuration by reducing thecomplexity of the base station scheduler. To make the most of theeffects of both method 1 and method 2, the method of determining N interminal 200 according to method 3 may be configured as follows.

After setting a static or quasi-static lower limit value to a possiblevalue of N, when PUCCH resources are shared among a plurality of ePDCCHsearch space sets set in the terminal, terminal 200 designates the scaleof the smallest ePDCCH search space among a plurality of ePDCCH searchspace sets set in the terminal sharing the PUCCH resources as the valueof N. However, when this value falls below a lower limit value, thevalue of N is set to the lower limit value. It is thereby possible toreduce the overhead of PUCCH while reducing constraints on schedulingfor future subframes due to the multiplexing of PUCCH with many DLsubframes within one PRB.

(Method 4)

According to method 4 in contrast to method 3, when sharing PUCCHresources among a plurality of ePDCCH search space sets after setting anupper limit value, terminal 200 designates the scale of the largestePDCCH search space among a plurality of ePDCCH search space sets set inthe terminal sharing PUCCH resources as the value of N. That is, themethod of determining N in terminal 200 according to method 4 is asfollows.

After setting a static or quasi-static upper limit value to a possiblevalue of N, when PUCCH resources are shared among a plurality of ePDCCHsearch space sets set in the terminal, terminal 200 designates the scaleof the largest ePDCCH search space among a plurality of ePDCCH searchspace sets set in the terminal sharing the PUCCH resources as the valueof N. However, when this value exceeds an upper limit value, the valueof N is set to the upper limit value. It is thereby possible to reduceconstraints on scheduling for future subframes due to the multiplexingof PUCCH with many DL subframes within one PRB while reducing theoverhead of PUCCH.

(Method 5)

According to method 5 in association with method 2, the value of N isset to a maximum value of PUCCH that can be multiplexed with one PRB.That is, terminal 200 sets the value of N based on equation 19. Here,Δ_(PUCCH_OFFSET) represents the amount of offset of PUCCH to be mappedwithin one PRB and is a value set in advance by base station 100. SinceHARQ-ACKs arranged on PUCCHs in one PRB correspond to only downlink datain one DL subframe, it is possible to avoid constraints on schedulingfor future subframes due to the multiplexing of PUCCHs with many DLsubframes within one PRB.[19]N=36/Δ_(PUCCH_OFFSET)  (Equation 19)

(Method 6)

As described in method 1, the scale of ePDCCH search space sets is 4, 8,16, 32 or the like, and since PUCCH resources are never dispersed if thevalue of N is divisible among a plurality of ePDCCH search space sets,PUCCH resources can be efficiently used. Thus, in method 6, the value ofN is equalized to the scale of the ePDCCH search space set. The presentmethod can be combined with one of methods 1 to 5.

A specific method of setting the value of scale N of a PUCCH resourceregion for each c′ and each m has been described so far for the casewhere the PUCCH resource region is shared among a plurality of ePDCCHsearch space sets.

Embodiment 3

In Embodiment 2, terminal 200 calculates c′ based on not only eCCE indexn_(eCCE) but also offset value δ_(ARI) in a virtual PUCCH resourceregion corresponding to m=m_(current) and then identifies PUCCHresources in the actual PUCCH resource region. In the presentembodiment, terminal 200 includes the ePDCCH-PUCCH resource regioncorresponding to not only m=m_(current) but also m<m_(current) in thevirtual PUCCH resource region.

As described above, parameter m is an index of a downlink communicationsubframe for one uplink communication subframe and sequentiallynumbered. Thus, parameter m corresponding to m<m_(current) means a pastDL subframe. Since DL scheduling in a past DL subframe is determined inthe current DL subframe, if there are any free PUCCH resourcescorresponding to PDCCH or ePDCCH in the past DL subframe, using the freePUCCH resources in the current DL subframe will impose no constraint onscheduling of future DL subframes.

In the present embodiment, an ePDCCH-PUCCH resource region whenm≤m_(current) as shown in FIG. 20 is designated as a virtual PUCCHresource region. FIG. 20 shows an example when m_(current)=2.

Here, if m≤m_(current), since the ePDCCH-PUCCH resource regioncorresponding to m=0 is most congested, the range of m may be limitedsuch as “m_(current) and m_(current)−1(m_(current)>0)” instead of“m≤m_(current).”

According to the present embodiment, more ePDCCH-PUCCH resources areincluded in the virtual PUCCH resource region than in Embodiment 1, andit is thereby possible to lower the possibility that the shifted PUCCHresources will be arranged outside the ePDCCH-PUCCH resource region dueto a shift based on an offset value indicated by ARI, and reduce thetotal PUCCH resource region.

Variations 1 to 7 shown in Embodiment 2 are also applicable in thepresent embodiment.

Embodiment 4

In Embodiment 2, terminal 200 calculates c′ based on not only eCCE indexn_(eCCE) but also offset value δ_(ARI) in the virtual PUCCH resourceregion corresponding to m=m_(current) and then identifies PUCCHresources in the actual PUCCH resource region. In the presentembodiment, terminal 200 includes an ePDCCH-PUCCH resource regioncorresponding to not only m=m_(current) but also m=m_(special) when theoccupancy of the PUCCH region is low, in the virtual PUCCH resourceregion.

As shown in FIG. 3, there are special subframes indicating switchoverfrom a DL subframe to UL subframe in TDD. A special subframe is composedof several symbols for downlink communication (DwPTS: Downlink PilotTime Slot), a gap and several symbols for uplink communication (UpPTS:Uplink Pilot Time Slot). In DwPTS, downlink data communication may beperformed as in the case of a downlink communication subframe. In UpPTS,SRS (Sounding Reference Signal) transmission or PRACH (Physical RandomAccess CHannel) transmission may be performed. In a special subframe,available PDCCH region and PDSCH region are smaller than those in otherDL subframes. Thus, there are fewer terminals to which PDSCHs areassigned in the subframe.

When a HetNet environment combining a macro cell and a pico cell isassumed, ABS (Almost Blank Subframe) is defined in which PDCCH and PDSCHare not assigned in downlink subframes in the macro cell in order toavoid interference from the macro cell to the pico cell. There are noPDCCH-PUCCH resources in the subframe.

Thus, in a special subframe or ABS, the occupancy of PUCCH by PDCCH islocally lowered. Therefore, in the present embodiment, ePDCCH-PUCCHresources are positively arranged in the PUCCH region whose occupancy islocally low. This allows free resources to be effectively used.

FIG. 21 illustrates a case where m_(current)=2 and special subframem_(special)=0. Here, m=0, 1 and 2 in FIG. 21 correspond to SF #1, 5 and6 in UL-DL Configuration #3 in FIG. 3.

In this case, an ePDCCH-PUCCH resource region corresponding toM=m_(current)=2 or m_(special)=0 is defined as a virtual PUCCH resourceregion.

Variations 1 to 7 shown in Embodiment 2 are also applicable in thepresent embodiment.

Embodiment 4 may be operated in combination with Embodiment 3. That is,the ePDCCH-PUCCH resource region corresponding to m≤m_(current) andm=m_(special) can also be defined as a virtual PUCCH resource region.

The embodiments of the present invention have been described so far.

The above description has focused on the avoidance of collision betweenPDCCH-PUCCH and ePDCCH-PUCCH, but the present invention is alsoapplicable for the avoidance of collision between ePDCCH-PUCCH in anePDCCH terminal and PUCCH in a UL CoMP terminal in addition to theavoidance of collision described above.

FIG. 22 illustrates a case where when an ePDCCH terminal and a UL CoMPterminal exist in a HetNet environment, the UL CoMP terminal receivesPDCCH (ePDCCH) and PDSCH from macro eNB and transmits PUCCH to pico eNB.When the ePDCCH terminal and UL CoMP terminal transmit PUCCHs using thesame PRB, even when PUCCH resources orthogonal to each other within thesame PRB are used for PUCCHs, interference due to a difference inreception timing of a plurality of PUCCHs in pico eNB or interferencedue to a difference in PUCCH receiving power (far-near problem) occurs.This is attributable to the fact that while the UL CoMP terminalperforms downlink communication with macro eNB, the UL CoMP terminalperforms uplink communication with pico eNB.

In order to avoid such interference, PUCCH resources need to be shiftedby at least one PRB. FIG. 22 illustrates method 1 and method 2 as such amethod.

In method 1, the entire ePDCCH-PUCCH resource region is offset andresources completely different from a PUCCH resource region for COMP areused to thereby avoid interference. Method 1 can easily avoidinterference, but meanwhile, there is a problem that the overhead ofPUCCH resources in total is large.

Thus, method 2 shares the ePDCCH-PUCCH resource region and the CoMPPUCCH resource region to reduce the overhead of PUCCH resources intotal. In this case, in order to avoid interference, a shift is madebased on an offset value indicated by ARI. Here, in order to realize atleast one PRB shift, when the number of PUCCH resources per PRB is 18,the offset value needs to be set to 18 or above. For this reason, thepossibility that the offset destination PUCCH resource may becomem>m_(current) is higher than in the case with “+1” which is an offsetvalue applied in the PDCCH-PUCCH resource region. That is, there areproblems similar to the problems to be solved in the present invention.That is, constraints are generated on scheduling of future DL subframesand collision between PUCCH resources occurs (however, in the case ofFIG. 22, collision between ePDCCH-PUCCH resources and CoMP PUCCHresources instead of collision between ePDCCH-PUCCH resources andPDCCH-PUCCH resources).

The present invention is applicable not only to a case where collisionoccurs between ePDCCH-PUCCH resources and PDCCH-PUCCH resources orbetween ePDCCH-PUCCH resources and UL CoMP PUCCH resources, but also toa case where collision occurs between ePDCCH-PUCCH resources betweendifferent ePDCCH terminals. That is, the present invention is applicableto a case where collision occurs between PUCCH resources betweendifferent terminals and where ePDCCH-PUCCH resources are used in atleast one terminal.

Although an antenna has been described in the aforementionedembodiments, the present invention may be similarly applied to anantenna port.

The term “antenna port” refers to a logical antenna including one ormore physical antennas. In other words, the term “antenna port” does notnecessarily refer to a single physical antenna, and may sometimes referto an antenna array including a plurality of antennas, and/or the like.

For example, how many physical antennas are included in the antenna portis not defined in LTE, but the antenna port is defined as the minimumunit allowing the base station to transmit different reference signalsin LTE.

In addition, an antenna port may be specified as a minimum unit to bemultiplied by a precoding vector weighting.

In the foregoing embodiments, the present invention is configured withhardware by way of example, but the invention may also be provided bysoftware in cooperation with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

As described above, a terminal apparatus according to the embodimentsdescribed above is a terminal apparatus including: a control sectionthat arranges a response signal on a predetermined PUCCH resource in anuplink control channel (PUCCH) resource region corresponding to anenhanced downlink control channel (ePDCCH); and a transmitting sectionthat transmits the response signal arranged on the PUCCH resource, inwhich the PUCCH resource region is divided into a plurality of partialregions, and each of the partial regions is divided into a number ofdownlink communication subframes, PUCCH resources for each index c′ ofthe partial region and each index m indicating a time-sequential orderof the downlink communication subframe are arranged in the PUCCHresource region in ascending order of indices m and in ascending orderof indices c′, and the control section arranges a response signalcorresponding to an m-th downlink communication subframe in a PUCCHresource selected from among the PUCCH resources corresponding to theindices m and below.

The terminal apparatus according to the embodiments described above,further includes: an error detection section that detects an error ofdownlink data in each downlink communication subframe transmitted from abase station apparatus; and a generating section that generates aresponse signal indicating the error detection result for each downlinkcommunication subframe, in which the control section arranges a responsesignal indicating the error detection result in an m-th downlinkcommunication subframe in a PUCCH resource selected from among the PUCCHresources corresponding to the indices m and below.

In the terminal apparatus according to the embodiments described above,the control section arranges a response signal corresponding to the m-thdownlink communication subframe in a PUCCH resource selected from amongthe PUCCH resources corresponding to the index m or PUCCH resourcescorresponding to indices of downlink communication subframes to whichfewer ePDCCHs are assigned than to other downlink communicationsubframes.

In the terminal apparatus according to the embodiments described above,the control section calculates the index c′ in a virtual PUCCH resourceregion in which PUCCH resources corresponding to downlink communicationsubframes are collected and determines a PUCCH resource on which theresponse signal is arranged.

In the terminal apparatus according to the embodiments described above,the control section calculates the index c′ based on a leading eCCEindex occupied by the ePDCCH intended for the terminal and an offsetvalue indicated from base station apparatus and determines a PUCCHresource on which the response signal is arranged.

In the terminal apparatus according to the embodiments described above,when the PUCCH resource determined based on the eCCE index and theoffset value is not included in the PUCCH resource region, the controlsection includes a PUCCH resource on which the response signal isarranged in the PUCCH resource region by circulating the PUCCH resourcein the virtual PUCCH resource region or inverting the PUCCH resource atan end of the virtual PUCCH resource region.

In the terminal apparatus according to the embodiments described above,when the PUCCH resource determined based on the eCCE index and theoffset value is not included in the PUCCH resource region, the controlsection determines a PUCCH resource on which the response signal isarranged in a region other than the virtual PUCCH resource region.

In the terminal apparatus according to the embodiments described above,when the index c′ is smaller than a predetermined threshold, the controlsection determines a PUCCH resource on which the response signal isarranged based on a positive offset value in a direction in which theindex m and the index c′ increase, and when the index c′ is greater thanthe threshold, the control section determines a PUCCH resource on whichthe response signal is arranged based on a negative offset value in adirection in which the index m and the index c′ decrease.

In the terminal apparatus according to the embodiments described above,the control section calculates the index c′ based on a fixed valueindicated from the base station apparatus and determines a PUCCHresource on which the response signal is arranged.

In addition, a base station apparatus according to the embodimentsdescribed above is a base station apparatus including: a control sectionthat determines whether or not a predetermined PUCCH resource in anuplink control channel (PUCCH) resource region corresponding to anenhanced downlink control channel (ePDCCH) collides with anotherresource; a control information generating section that generatescontrol information for identifying a non-colliding PUCCH resource for aterminal apparatus; and a transmitting section that transmits thecontrol information, in which: the PUCCH resource region is divided intoa plurality of partial regions, and each of the partial regions isdivided into a number of downlink communication subframes, PUCCHresources for each index c′ of the partial region and each index mindicating a time-sequential order of the downlink communicationsubframe are arranged in the PUCCH resource region in ascending order ofm and in ascending order of c′, and the control section determinescollision or no collision with another resource among PUCCH resourcescorresponding to the indices m and below.

A transmission method according to the embodiments described above istransmission method including: making a control to arrange a responsesignal on a predetermined PUCCH resource in an uplink control channel(PUCCH) resource region corresponding to an enhanced downlink controlchannel (ePDCCH); and transmitting the response signal arranged on thePUCCH resource, in which: the PUCCH resource region is divided into aplurality of partial regions, and each of the partial regions is dividedinto a number of downlink communication subframes, PUCCH resources foreach index c′ of the partial region and each index m indicating atime-sequential order of the downlink communication subframe arearranged in the PUCCH resource region in ascending order of m and inascending order of c′, and in the making a control, a response signalcorresponding to an m-th downlink communication subframe is arranged ina PUCCH resource selected from among the PUCCH resources correspondingto the indices m and below.

The disclosures of the specifications, drawings, and abstracts inJapanese Patent Application No. 2012-172348 filed on Aug. 2, 2012, andJapanese Patent Application No. 2012-209810 filed on Sep. 24, 2012, areincorporated herein by reference in their entireties.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in mobile communicationsystems compliant with LTE-Advanced.

REFERENCE SIGNS LIST

-   100 Base station-   200 Terminal-   101, 208 Control section-   102 Control information generating section-   103, 105 Coding section-   104, 107 Modulation section-   106 Data transmission controlling section-   108 Mapping section-   109, 218 IFFT section-   110, 219 CP adding section-   111, 222 Radio transmitting section-   112, 201 Radio receiving section-   113, 202 CP removing section-   114 PUCCH extracting section-   115 Despreading section-   116 Sequence controlling section-   117 Correlation processing section-   118 A/N determining section-   119 Bundled A/N despreading section-   120 IDFT section-   121 Bundled A/N determining section-   122 Retransmission control signal generating section-   203 FFT section-   204 Extraction section-   205, 209 Demodulation section-   206, 210 Decoding section-   207 Determination section-   211 CRC section-   212 Response signal generating section-   213 Coding and modulation section-   214 Primary-spreading section-   215 Secondary-spreading section-   216 DFT section-   217 Spreading section-   220 Time multiplexing section-   221 Selection section

The invention claimed is:
 1. A base station comprising: a transmitter,which, in operation, transmits downlink control information (DCI) mappedin a search space set of a physical downlink shared channel (PDSCH); anda receiver, which, in operation, receives a response signal on aphysical uplink control channel (PUCCH) resource, the PUCCH resourcebeing determined based on a control channel element (CCE) index to whichthe DCI is mapped and a first offset value, wherein the first offsetvalue is determined from a plurality of offset values including avariable offset, the variable offset being calculated using a formulathat includes a parameter relating to a size of the search space set,the size of the search space set for a special subframe is smaller thanthe size of the search space set for a non-special subframe, thevariable offset is a negative value, and the first offset value isdetermined based on information relating to an ACK/NACK resource of theDCI.
 2. The base station according to claim 1, wherein the PUCCHresource is determined based additionally on a second offset valuedifferent from the first offset value.
 3. The base station according toclaim 2, wherein the second offset value specifies a starting point of aPUCCH resource region.
 4. The base station according to claim 1, whereinthe size of the search space set for a special subframe is a half of thesize of the search space set for a non-special subframe.
 5. Acommunication method comprising: transmitting downlink controlinformation (DCI) mapped in a search space set of a physical downlinkshared channel (PDSCH); and receiving a response signal on a physicaluplink control channel (PUCCH) resource, the PUCCH resource beingdetermined based on a control channel element (CCE) index to which theDCI is mapped and a first offset value, wherein the first offset valueis determined from a plurality of offset values including a variableoffset, the variable offset being calculated using a formula thatincludes a parameter relating to a size of the search space set, thesize of the search space set for a special subframe is smaller than thesize of the search space set for a non-special subframe, the variableoffset is a negative value, and the first offset value is determinedbased on information relating to an ACK/NACK resource of the DCI.
 6. Thecommunication method according to claim 5, wherein the PUCCH resource isdetermined based additionally on a second offset value different fromthe first offset value.
 7. The communication method according to claim6, wherein the second offset value specifies a starting point of a PUCCHresource region.
 8. The communication method according to claim 5,wherein the size of the search space set for a special subframe is ahalf of the size of the search space set for a non-special subframe. 9.An integrated circuit comprising: circuitry, which, in operation,controls: transmitting downlink control information (DCI) mapped in asearch space set of a physical downlink shared channel (PDSCH); andreceiving a response signal on a physical uplink control channel (PUCCH)resource, the PUCCH resource being determined based on a control channelelement (CCE) index to which the DCI is mapped and a first offset value,wherein the first offset value is determined from a plurality of offsetvalues including a variable offset, the variable offset being calculatedusing a formula that includes a parameter relating to a size of thesearch space set, the size of the search space set for a specialsubframe is smaller than the size of the search space set for anon-special subframe, the variable offset is a negative value, and thefirst offset value is determined based on information relating to anACK/NACK resource of the DCI.
 10. The integrated circuit according toclaim 9, wherein the PUCCH resource is determined based additionally ona second offset value different from the first offset value.
 11. Theintegrated circuit according to claim 10, wherein the second offsetvalue specifies a starting point of a PUCCH resource region.
 12. Theintegrated circuit according to claim 9, wherein the size of the searchspace set for a special subframe is a half of the size of the searchspace set for a non-special subframe.